Debit order payment not processed and now they claim non-payment

I took out a loan with RCS and have been paying via debit order since inception. I received a call an agent stating that my account is in arrears as the debit order for 25 August did not go through. I then tell them it's impossible as the debit order date falls on my salary date. They tell me that the debit order went off and was returned unpaid. Again...IMPOSSIBLE as debit order falls on my salary date. Furthermore, there is no record of them debiting my account on 25 August and the debit order being reversed. I then get a letter saying that there is no debit order on my account but I've been paying it via debit order since inception and have not cancelled it!!!! VERY RUDE call centre agent tells me to wait for the next month to see whether it goes off or not and I tell her that will adversely affect my credit report. She proceeds to tell me in the rudest of tones that it's already ruined! When I insisted on talking to a manager I was put on hold for 30mins! DISGUSTED AT THE SERVICE!!!! ABSOLUTELY SHOCKING!!!!!!