Jet Payment Received But not credited into my account

I made a payment of R300 on the 18th of March at Jet Durban West Street. Till today that R300 is not credited into my account but I have a receipt of payment. I called Jet call centre several times being given different emails to send proof of payment to still nothing is done. Sent an email to RCS who has now taken over Jet accounts n they as well not helping. How had can it be to trace my payment as I still have the receipt. No one is bothered to contact me, I have to contact them. I want to close this account but I won't pay the balance without the R300 being credited into my account.