RCS Credit cannot be stopped

We bought an inverter on the RCS Credit Card. We got 6 months to pay, then no interest would be charged. After a struggle they have'nt received all our payments. After that we went to GAME Store to sort this out, after several e-mails we sent all the proof of payments to finalize this account. Still the 8th of March the sent a sms stating I still owe them R 193.24. We sent a huge e-mail AGAIN!!! On 12th of March 2024, they sent another sms stating I now owe R 334.68?????? How????? This is unacceptable. It is as if they do not care if we sent an e-mail or don't listen, they just go on and on....