BANK MAKING ACC CHANGES WITHOUT INFORMING CLIENT

I received an email yesterday stating that my home loans acc is in arrears and has been short paid, since May 2015. I contacted the collections dept who informed me that there's been a change in monthly payment and that account is in arrears. This after I have just arranged and paid up the previous arrears amount. I haven't received anything in writing or don't recall me agree to any changes in monthly payments. Who must take responsibility for the new arrears amount, if I was never informed in writing of changes that was made.? When I asked for that, I was told that there's a delay in post, but its funny that I received the email yesterday. Mark Radley also mentioned that the debit orders are being returned, but I don't even have a debit order instated, I pay via eft monthly, and before then I used to pay it otc at my branch. I'm also told that the acc was previously with legal, so that is why there's a change, but I don't think payments can be changed according to an institution, without contacting the relevant clients. I think I have a lot of reasons to be upset. He also said he will note on the system that I refuse to make arrangements to repay. I am utterly disgusted by stdbnk