Terrible experience

I payed my credit installment on the 30th of November, received notifications saying that my account is in arrears, after going back and forth with customer service with several phone calls they eventually asked me to send proof or payment, I sent a bank statement and my receipt but still no outcome till now, they not even replying to my email to acknowledge this issue, it's taking so long for them to resolve the issue even though I sent in the relevant documents that now my account is in arrears and I'm getting charged for collection fees which is just running up my bill, I always pay my bill early and I don't think this is fair, I have emailed the ombudsman and currently waiting for feedback