MTN south africa lack of service

Hello i am very disappointed in mtn and there customer service. They upgraded the incorrect number and i have been calling them for the past 5 months just to find out 3 weeks ago there is no record of my calls and they over charged me because of upgrading the incorrect number. They said they will provide me with a credit note and keep om saying they will call me back but no reply and not credit note. I am highly disappointed and not to get a call back after phoning, emailing and Facebook message for the past 5 months.