Poor service

I have a problem with MTN blacklisting me for a service I didn't receive just because I reversed the money they deducted,They offered me a good deal on a sim card contract but when the SIM card was delivered it wasn't registered,I sent communication but didn't get help and I have been sending communication that the SIM card they sent me isn't registered yet they took my id copy and proof of registration,no one ever called me to ask why I reversed the money but now they blacklisted me and I am the one who has been communicating they just forward my emails to Mondo and the legal department saying they are investigating but nothing has been done yet and it's been 2 year's now,I am blacklisted yet I pay my accounts on time only this company is ruining my life and doesn't want to account for it now MBD agents are calling me everyday because Mondo still says I owe them and I do not since they didn't offer me any service.