********* conduct

I used to pay my instalments every month by debit order, but for some reason the debit order stopped. So when this happened I decided to continue paying cash, sometimes I'd pay more than the instalment due but to my surprise I'm threatened by calls from their collections dept. I don't understand why I'm being treated like a ******** or payment defaulter. I have tried to engage with them telephonically but instead the I'm met with arrogance. What they are doing is putting my credit profile at risk. According to my understanding, if you pay cash the payment reflects same time or same day but still they would still harass me 4days after I have made payment.