Bad service ever

I opened an account at Mr price 2018 and this year I decided to close it early this year. However they are still sending me invoices like i am still owing them. They have sent me an sms that my account is paid up but to my surprise they appearing on my credit report. On the invoices they are send me the amount is accumulating therefor my credit score is being lowered by this. I am fed up with their actions because I have called them countless times ask them to remove me on their database as their client but they failed to do so.