Upgrade - Credit Limit

After harassing me for several months MTN persuaded me to upgrade last week. I upgraded to MTN's top package - MTNSky. Before upgrading my credit limit was R20,000 as I run my business from my cellphone. After the upgrade my credit limit was decreased to R5,016 and subsequently my line was suspended rapidly for reaching the credit limit. I contacted the accounts department which informed me that I have to wait three months before they can increase my limit or alternatively I can visit a MTN store with my payslip and maybe they will be willing to increase the limit. I have had an average spend of R4,500 per month for the past two years without any default in payment and now they insult me by asking for my payslip. I asked to speak to a manager and I was told that all the managers in MTN is in meeting and that I should send a mail which will be answered within 24 hours. Luckily Cell C is offering a buy out which seems very attractive right now.