Collection charged on acc after timeious payment

I paid my loan acc on 30/4/15 before the agreed date of the 1st of every month. On the 4th of May I received a call from the company to say that they did not get my payment. I received my statement this month and picked up there was a collection charge added to my acc of R171.72 and tried to get hold of the customer services dept to sort this out but nevertheless was placed on hold for 30 minutes and still did not speak to an agent yet. I feel this is very unfair to add charges to my acc, especially after I've never missed an payment and got proof that I made the payment on 30/4/15 IN TIME. I called the call centre twice and the call was dropped twice so that is why I decided to get reaction on hellopeter. This is pathetic service if you cannot even get hold of an agent to speak to what is the use of being open from 8H00 to 20H00 daily and there is no customer service?