REFUND DUE TO ME

I made an overpayment almost 3 months ago of R500. I have no money owed to the company but accidently paid it into their bank account. I am a pensioner and have been submitting forms about 6 times to proof the over payment, bank statements, proof of payment, copy of ID.

Do not know what to do anymore to get my R500 back. It is ridiculous for such a big company to refuse to refund a persons money that does not belong to them.