Poor treatment from MTN

In late January I received a call from an MTN agent offering me a "special" upgrade with a Microsoft cell phone. It seemed like a good deal until I researched the phone and established if did not have an Android operating system, so I called MTN and cancelled as my existing Samsung Galaxy is a superior phone. The cancellation was accecpted but days later their delivery courier called me to arrange delivery. I again called MTN and was told not to accept delivery, so I comp****. In Feb I received an invoice for the first month's subscription R91.10 as well as the sub for my existing contract. I called MTN and explained the situation and was told a credit would be passed within 72 hours. On March 29 my bank a/c was debited with R232.07 which is my normal debit PLUS R91.10, despite being told that the latter amount would be credited. In addition my April invoice reflects a "termination charge" of R2678.88! As a loyal client of many years standing I feel this is disgusting treatment and if not resolved will force me to migrate to a competitive service provider