Negligent and poor service

I'm very, very disappointed in MTN customer service. I had a contract with them back in 2017 paid it up finish, now all of a sudden I'm in arrears for something I paid up during that fixed term. Tried calling the contact center I've been put on hold for more than an hour being sent to one department to another only for my call to be dropped. I'm very frustrated this is messing up with my credit score for something done by you. Mtn is a ****.