Graduation programs in distance mode after Polytechnic Diploma course

You can do AMIE by examination from Institution of Engineers, India. The course is considered equivalent to B.Tech/B.E for all practical considerations. You can go for M.Tech after completing AMIE. You can apply all jobs where the eligibility criteria is a graduation in Engineering.

You can do many other graduation courses like BA, B. Com or B.Sc by correspondence course. There are many universities in India offering these courses by correspondence course. IGNOU is one such very famous university.. You can apply to those courses and complete them by correspondence course.

With the qualification of your diploma consisting of three years( according to my assumption), you can take up the course of AMIE which is regarded as equivalent to BE for all practical purpose especially in relation to employment or for the persuasion of post graduate course in Engineering. Moreover this degree is approved by the ministry of HRD and has got AICTE approval essential for a technical degree.
However, you have not indicated the stream with which you have comported your diploma.
If you are looking out Industrial Engg Department, specialisation in the same stream can be taken up in your section B course dealing with the specialisation in Engg. Section A consisting of eight papers has to be cleared first and then you have to clear nine papers included in section B. Best part while doing this course is you can clear the papers instalment wise depending upon your convenience of time after your duty - hours.
To strengthen your concept, you may take the help of professional institute providing you right guidance in the preparation of course.
This degree will widen your job - prospects.

Try to focus on your job and also on your studies. you have not specified that the job you are doing whether is a private or a govt job.
whatever it is try to put your best in your work. As the experience certificate is really important thing in case of job.
now I am answering the later part of your question. You can pursue AMIE which is a valuable course for industry related job. You can do masters in your near future also.

You have already completed a polytechnic diploma and are in an industrial job. Now you want to enhance your academic or technical qualifications for improving your career further in the same industrial unit or some other organisation.

This is a point at which a decision is to be taken for the stream you want to go ahead and in this context I want to say that you must identify your area of interest. From your resume it appears that you might be interested in a technical qualification but there are many other options which you can consider at this juncture.

The foremost option in correspondence mode is going for AMIE but that is not the end. If you have interest in commerce, you can think of doing B.Com. after which you can try for many jobs in the industrial, commercial and business arena. If you have interest in science or humanities and want to explore the area of teaching then there are opportunities to do so after B.Sc./ B.A. and then B.Ed. There is another line that is computer science and if it fascinates you then you can do B.Sc. in computer science followed by some course in prospective fields like web designing, system management, data base etc. If you are good in studies then there is another option that after the graduation you can appear for so many competitive exams where if you compete you can carve out a very good career for yourself. These competitions are held in the areas of banking, state services, subordinate services, Railway services, defence services etc. So, you have to assess your capabilities and capacities vis-a-vis the various career making streams in our country.

Once you acquire additional qualifications you will have opportunity to join some start up groups or start at your own some business which has a potential for growth and slowly you can expand your work. We generally think for some job but today the job conditions in our country is not good. There are few jobs and many contenders. So, those who have innovative ideas and will to work hard can venture in the business areas and soon can be a self employed person. So work hard and keep your eyes open for such opportunities whenever come your way.

Please note that sometimes we feel that the grass is greener at the other side of fence but it might be an illusion. So, one should also explore the possibilities of going up in ones present organisation after acquiring additional qualifications. Sometimes there are good breaks people get there itself.

As you have done your class XII with PCM, I will advise you to go for B.Sc. or B.Sc. computer science as per your interest and aptitude. If it suits you then it can be converted in a career path by doing certain short term courses (like MS office or system management etc) in computer science and then trying a job in the industry. After these courses one can get a variety of jobs as every office or business unit wants people having expertise in computer handling and working. Even a small business unit uses a computer for keeping the records and in that light getting a computer assistant or assistant job in the industry will be much easier after this qualification.