I'v been a customer with MTN for many years now and recently we have been receiving calls from MONDO who is working with MTN doing upgrades

I'v been a customer with MTN for many years now and recently we have been receiving calls from MONDO who is working with MTN doing upgrades. Last year I received a call from them to upgrade my line and they changed the entire package that I was on which is absolutely no use to me. I lodged a complaint last year already and still waiting for them to correct it. When you call in they forever offline and never return calls. The staff is rude and have that don't care attitude! This is extremely irritating as you call MTN and they say call MONDO and visa versa! Where do we turn to now?