INTEREST

I have a signed debit order with Nedbank to deduct in full each months purchases done on my credit card. This has been the practise for the last 6 years. The last 2 months I noticed that interest was charged and phoned the credit card customer services, spoke to Lerato who was unable to provide me with why interest was being charged when the amount reflected monthly gets paid in full. I requested that I be phoned by someone working with my account who would be able to answer my questions. Nobody phoned. Couple of days later I again brought this to attention but again nobody phoned. I send a e_mail on 10 April 2015 and still no acknowledgement or respons. Seems interest is charged at random and when queried nobody wants to deal with the issue.?? Also it seems the credit division does not adhere to the broader Nedbank policy who prides themselves in only having to ask once. It seems the credit division has a policy of NOT/NO RESPONS.