Contract upgrade

I am very unhappy with the service I received; I have tried multiple times to speak to a consultant regarding one of my contracts with MTN, I woke up one morning and 70gig of my data is gone no one can assist me to where the data went even though I have Wi-Fi everywhere I go. I MTN consultant gave me a call around 2 weeks ago to upgrade one of my plans I agreed for the 50-gig summer plan, this morning when I check my App the totally wrong plan is billed to me. I have been I very loyal client of MTN over the last 6 years, but this is very unacceptable.