Mtn poor service and ****ming people

I have a contract with MTN and I have been paying in advance so the took advantage and take more than what I have signed up for, I call them and they say it’s tax added, they making me a fool and they block my number, I can’t make calls or use the airtime and no one is willing to assist. They also says all calls are recorded however they failed to provide the information or the recorded calls. I once open a complaint against them