Clarity about caste system that I am facing in the current situation

Your father is OC. Your mother is SC.
As per the 1975 G.O., the children can be given as per the caste of the father or the mother, based on the declaration of the parent/ Parents.
The GO says,
"shall be considered to belong to either the community [SC/MBC/BC or OC] of the father or mother according to the declaration of the parents regarding the way of life in which the children are brought up".
In your case, your father left you both and you were with your maternal grandfather and maternal uncle. They belong to SC. So if your mother gives a declaration about her caste and that you were brought up by her, you can claim SC caste. But they may ask about Christianity. SCs who got converted to Christianity may be treated as BC only. SO you have to clarify that your naming is done by your father but you are not a Christian. Then they may consider. If they don't consider your BC C certificate only will become the final. You have to contact the MRO of your area to get this certificate.

Respected sir, I really feel grateful for your suggestion, however u asked me to take declaration from my mother regarding her caste and that she brought me up but she is not there sir she expired in the year 1998. So what should be done in this case sir.

You are entitled to choose the caste of your mother or father as you wish but as they are not alive the problem would come in validating that and getting that confirmed. The only way that I can think this possible is by giving some legal affidavit and getting that certified under the seal of a notary public or first class magistrate. So, better option in this case will be to consult a lawyer who will be able to give guidance in preparing such affidavits and they might also need some gazette notification or advertising in the local papers also but all those procedures and processes are to be legally completed so that you can get that benefit by switching over to your mother's cast. You might require some witnesses like the close relatives or other people from the society who knew your family in one way or other to facilitate you for making those affidavits valid and authentic. Please take care in keeping all your documents in a chronological manner and everything will be asked to be annexed with the affidavit to make it self sufficient document for need of caste classification by the local administrative machinery of the concerned office from where the caste certificates are generally issued and rectified in your area.

According to the 1975 G.O.: " Children shall be considered to belong to either the community of the father or mother according to the declaration of the parents regarding the way of life in which the children are brought up".

A letter issued by Union Social Justice and Empowerment Ministry to Chief Secretaries of all State Governments and Union Territories said, "In cases where a child has been brought up in surroundings of a notified community to which the mother belongs to and has suffered the deprivations, indignities, humilities and handicaps like any other member of that community, then such a child of separated/divorced/single women has to be treated as a member of the scheduled caste community and would be entitled to receive benefits as such."

I think you are entitled to avail of S C benefits. I advise you to consult a good lawyer.

As mentioned above, your father and mother belong to a different community and you are in a dilemma as to which community I should choose. I think you will have to follow government rule. As per 1975 G.O "Children shall be considered to belong to either the community of the father or mother according to the declaration of the parents regarding the way of life in which the children are brought up". Hence, following govt rules, you should choose your mother caste as some relatives are there and so it would be a little bit easy to make a caste certificate and other important documents which can be demanded in future for a different aspect. If you choose the father side then the problem would be more because there you don't know anybody. You would need some close relative to make affidavits valid and authentic which would difficult in the case of the father community.
For better clarification, you should consult a lawyer because your entire process would be solved through the legal process.

In your case, you are free to choose either of the caste- your mother or the father. In your case, you have developed an ambiguity how you should proceed for making a caste certificate. The best recourse in this case would be to approach a lawyer and his advice is to be followed. You will have to produce the photocopies where your mother's name is appearing being your guardian. The lawyer would make a draft to be signed by the rotary magistrate. In the same certificate, you would be required to put your signature even which will ultimately be attested by the Magistrate. Once the affidavit Certificate is released through the court after the necessary formalities. Get it published in a leading English paper apart from the local one. Preserve the cutting of the paper so that it could be shown to the officials wherever such a situation arises.