Frustrated and cant describe the anger

I had a complaint last year December about my MTN account that had problems. I cannot understand for a company this huge that there staff can be so unreliable and f...up a persons account like they do. In February I recieved a statement stating that my balance is R0,00 asumming the account has been closed due to the huge volume amount of airtime not being used. I requested a credit report and discovered that I have been handed over. For the Love of Christ I do not know and as to why I cannot think that if something was wrong with my account that they would contact me. Via email or contact details. Today I recieved a invoice saying I am 4 payments behind with a total of R1500 to be paid. How in the blazes can a person get these people to fix your account and do there DAMN work. Getting a hold of them is a nightmare. Please help me with this. No person has money to just cough up when they demand money and for my credit score I think that there is nothing one can do.