FNB robbing their loyal customers

Hi, an agent called me and sold me a cellphone contract and the billing they promised is wrong, I have been calling since last year to query and still it hasn't been resolved so I tried to cancel a contract then with them but I haven't had any help. I am a loyal customer of FNB and this thing that is going on is hurting. please treat your customers with respect please. don't know how many times I have laid complaints to deaf ears.