Billed for service that is terminated

Bad customer service to the highest degree. My contract ended on the 11th of May and I called to make sure the contract is cancelled. I was confirmed that the contract is canceled but mtn keeps on billing me for nothing, no service. Their call center it's the worst nightmare you only get assistance when you want to open a contract because they are all about ma money and not respecting clients they make that money from. Mtn service for getting people to depts it's top range but once mtn get people into contract their service is extremely sneaky and poor,all mtn wants is money at all cost. Extremely bad experience