Contract terminated however blacklisted

I had a contract with mtn for data sim card. I was paying R500 Monthly. The card always had no network. I would always send complaints and not getting help.

They always advised me to take out the sim card from my rooter, still would not work. I paid the installment for 24months for nothing.

By February 2023 i sent them massage to cancel my contract. The contract was end in April 2023. I informed them in advance as they told me.

By May 2023 they took R1000. From my bank account. I asked them by message the reason of deducting my R1000. They never responded on me.

This year when i go for loan, i found out that i am blacklisted by them with an amount of R4000.

I went to their branches they are failing to help me.

I want them to clear my name and my R1000.00 deducted after termination of my contract.

Thank you so much.