Bad customer service and dishonesty

I took a contract in February 2018 and the contract stipulated I will receive 4G data day and 4G data night, I am have only received 2G data day. went to the Nelspruit riverside branch where I took the contract and was told the lady who helped resigned. the manager cant even help me, its a month two weeks waiting for feedback. I have been promised that I will be contacted for a solution I am not getting help. MTN is debiting my account while I'm not getting what I signed for. where do I go for help?