MTN, where are your manners ?

I have been a customer of MTN for at least 15 years, in December I changed my contract from a personal account to a business account, then the problems began......but I was unaware of them. I had an outstanding balance, but due to our local post office closing I wasn't getting my mail as it wasn't being sorted and sent to the post office I was supposed to be picking it up from. For the first time since December , on the 5th March I managed to pick up mail. I received an account from MTN, realised that there had been a mix up and paid R500 into the account on the 9th March with the intention of calling my branch later in the day to sort the balance out, as I wasn't sure exactly what it was I thought that I would pay something untill I knew the correct balance. I was called that same day by a debt collect agents, Munnik Basson and Dagma, a company with unpleasant agents, I tried to explain the mix up and that I had paid R500 and could they tell me the balance, they couldn't initially, I finally managed to get an email address and communicate by email, I have paid them the balance and hope that they leave me alone now. MY QUESTION TO MTN IS....... Why, after approximately 15 years of me being a customer of yours with no bad debts to you, yes I admit that there have been one or 2 times when I have forgotten to pay you .... you have then sent me an sms to let me know and I've paid straight away, we all forget things from time to time. WHY didn't you send me an sms or maybe have someone phone me to see what was wrong ... no... instead you send debt collectors, its sorted now but I'm so very disappointed in your customer service. I really would have hoped for better after being a customer for so long, and its not just one account our family has with your company...,we hold 6 contracts between us.....there is really only one reason why I stay with MTN and am not changing to another provider despite the lack of respect or just plain decency from MTN. Its the agent that has looked after our contracts for the last 10 years, he is amazing and he really is the ONLY reason we stay. Its certainly not your customer service or the signal for that matter either. Would it be at all possible for a senior manager to call or email me as I am interested to hear why you treat your customers in such a disrespectful manner.