Poor Service from MTN

I had an account of wifi router with MTN,the router didn't work since from delivery Jan 2023 ,Loged a call for investigation since then they didnt even help me to make the router work ,Then started from month end February 2023 receiving sms that I should pay R4201 through NuDebt management and I did that November 2023. So now I am blacklisted and all the mtn stores around me can't help me to get the paid up letter.I tried calling NuDebt management I dont get clear answer from them.

I can't open any account I can't do anything But I paid A non working router with a non registered Sim card inside R4201 My credit score is very poor because of MTN account . I am Strongly disappointed ..Poor Service MTN Poor Very Pooor

Please help me get help.