MTN has the ****test service and sales agents who lie to us

what **** business is MTN doing, I got a call from one of the sales consultants telling me that I have a reward as a loyal client, they are going to add more gigs to my sim that in my router and only R50 will be added but now my bill is and with almost R400, which I am very much not happy about it, I want to cancel all that because it is not what I agreed on..... the sales agents sucks because now their selling technique is the worst - even the home wifi they delivered does not work, I am actually paying for nothing.