MTN billing sucks

I have 6 contracts with MTN, which I upgraded in Dec. From Dec until today I have been querying my bill as MTN is charging me for devices when I did sim upgrades only. I have called the call centre, billings, retentions numerous times and no one can help me. All I get are reference numbers and escalations with no feedback or solutions. Its just a run around everytime I call wasting between 30 min to 2 hours on a call. Been a loyal customer for over 10 years but I am now appalled at the service.