How can I check my GEPF in RSAvia Internet before I decided to resign from my employer in 2017

no
simply because fixya site is not in the scam detection business

call your local taxation office or ask your accountant

I'd suggest writing a letter with the intent of keeping yourself in good regard with this employer even after you have gone. Employers do ring each other, and your new one just might do that. A letter like this might do (see sample)

https://www.seek.com.au/career-advice/how-to-write-a-resignation-letter
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Is this the correct site for you? :-)

ALWAYS thank your employer for all the opportunities they have given you. Remember, you need references from them in future, even if you dont need it right away.

Dear.....

It is with a heavy heart that I tender in my resignation.

I have enjoyed my time with the company and working directly with you (your line manager or direct supervisor).

After reviewing my career path and exploring other options, I have decided a move would further enhance my career.

I want to personally thank you and all those who have helped me along the way in achieving my goals.

I wish you and the company every success.

Yours truly

When writing a resignation letter, it's important to keep your resignation letter as simple, brief, and focused as possible. It should also be positive. Once you have made the decision to move on, there's no point in criticizing your employer or your job. Your letter of resignation should include information on when you are leaving. You can also let the employer know you appreciate your time with the company.
What to Include in Your Resignation Letter:
The fact that you are leaving and date when your resignation is effective.
Thanks to your employer for the opportunities you have had during your employment.
I'm going to include a link to a website that can show you some examples on how to construct your resignation letter, and some further helpful tips on what you might want to include.
Samples

You are free to resign if contract is due. Is there is a contract there are sometimes rules about resigning. Check on that.

I am pretty sure they do not want you to leave because you are an excellent employer. Take this to your advantage and get a good wage raise!!!

Ask for a raise and better working conditions, or a promotion.

God Bless You!!