Contract upgrade

I would like too file a formal complaint, I've been a loyal customer to mtn from 2013 but no longer can i take the mistreatment i get as a clint and how i have struggled to upgrade my contract at not one branch but 2 branches Columbine Square Shopping Centre and the glen shopping center firstly they never have stock of router's there new home wife , and if they do they cant find the product number on the system and its never corresponding and when they finally helped me at the glen mall the 12 th of November they couldn't even upgrade my contract form my old one u had to go back saterday sunday and monday and the router stil is not working there is no signal and when you complain they just say its not there fault, firstly how do you advertise a product that no branch wants to sell and thats not working, and its false advertise cause the product is not even operational client service is unacceptable