Appalling service

I have recently joined MTN from another service provider and the service since joining in January 2015 has been nothing short of appalling. I have been overcharged on every bill since signing the contract and when I go into an MTN store to ask for help, none of the store attendants have a clue what to do or they just tell me to phone 808. When I phone 808, the call is either placed on hold for up to 20 minutes with no answer or else it gets cut off. Often both of these occur. I must have phoned the call centre over 25 times now and they can never help me or just don't answer. I am sick of this pathetic service and i am on the verge of moving to another provider if it is not sorted out and the excess charge refunded to me.