No response from MTN since October, just another reference number!

I have been a loyal MTN customer for 15 years. In February 2018 I received a call from Summer Mobile for an upgrade. I never received any documentation or an upgrade, but MTN has upgraded me on their system and I have been duly charged for this "upgrade". I have been to numerous MTN stores, contacted the call centre and have sent numerous emails to MTN Customer Care. All I receive is another reference number. I have just received another sms from MTN stating that my line will be suspended if I do not make a payment. I refuse to make another payment before my account are rectified. Please help???