Pathetic Customer Service from MTN

I am struggling to get a hold of MTN legal for the past 17 days. I took out a contract in 2017 and paid every month until I was unemployed. My account was handed over to a debt collector and with an arrangement, I squared up my account and received proof from the debt collector showing a Nil balance. MTN sent me another statement saying that I owe them. I sent numerous emails asking what the outstanding balance is for, and I just never received any response from them. During this time I haven't received any statements nor calls from any agent. Two years later, I receive a call from a different debt collector stating that I owe them. I immediately started sending emails to MTN Customer Care, MTN Legal and the two debt collectors and STILL NO RESPONSE from MTN Legal. MTN is the worst service provider.