Service cancelled for not paying in time

Last month (April 2015), my debit order didn't went off, as there was insufficient funds in that account. I'm aware of this, and though I'll just receive a double bill this month, as with most other institutions. However, yesterday (18th May 2015), I received 2 notifications from MTN, asking me to make payment via ABSA, or service will be suspended. I did make payment for full outstanding amount, but still my service got suspended. What the ......? Trying to phone their call center (808), just says they experience high volumes - this since yesterday. Guess a lot of people are phoning to complain! So how do I get my service back up and running? Been a contract customer for more than 10 years, and this is how we're treated.