Disgusting business

I have had a contract with MTN for many years. In May this year I went for my upgrade. I told the consultant I spoke to, to cancel the insurance on my old device and have it transferred onto my new device. That was agreed to about a month thereafter this insurance started to bill me for 2 devices. The more I told them what had transpired the more they ignored me. Since then even tho I spoke to these people a hundred the more they do their own thing. Every month they suspend my line because of someone that is not doing their job properly. I don't owe them a thing I pay promptly every month. How does a person get through to the head of the department to sort this matter out. Everytime I phone I her pushed from pillar to post!! But this is how MTN treats their long term customers, as long as they can make money..I already threatened to cancel my insurance, in any case it's a lost course it doesnt work for one. I'm totally appalled by their treatment.