Unjustified Suspended line

MTN suspended my line twice this week for a mistake on their side due to migrating to a new system (Ilula). I resolved the issue on Monday however today my line was suspended again. MTN debited me twice in April on the 15 and 21, which made no sense why I should pay twice for 1 service. I reversed one premium and now they want me to pay R11 for the reversal even though they admit they weren’t supposed to debit twice. Why in the world would I have to pay for a mistake they made? I have missed a work telephonic meeting today as I have had no service on my phone, I visited the store to get help, I was told it was sorted but still nothing. I called them and was told it would take between 2-24hrs. How much more of an inconvenience should I suffer due to an error by this provider? Now I come across as being unprofessional because my phone goes to voicemail when my employer calls me for a scheduled meeting! It is absolutely unacceptable!