My loan servicer sent me to collections for a payment I made on time and I have the receipt and somehow that doesn’t matter

I need to write this out because I've now spent three weeks trying to fix this and I'm starting to feel like I'm in some kind of simulation. So back in September I made my monthly payment through my servicer's own portal, got a confirmation email with a reference number, screenshot it, moved on with my life. Standard stuff. Six weeks later I get a letter saying my account is delinquent and has been referred to a collections agency for nonpayment. I still have the confirmation email. I still have the screenshot. The payment cleared my bank account, I can see it in my statement with the date and the exact amount. The money left my account and went somewhere.

I called my servicer. First rep told me they had no record of the payment and I should contact my bank. I contacted my bank, they confirmed the transfer went through on their end and gave me a reference number. I called the servicer back with the bank reference number. Second rep told me the payment was probably applied to the wrong account and I should submit a written dispute. I submitted a written dispute with every document I had, confirmation email, bank statement, screenshot of the portal. Got a response two weeks later saying my dispute had been reviewed and my account remained delinquent. No explanation of where the money went. No acknowledgment of the documents I sent. Just the same form letter worded slightly differently. I have now been reported to the credit bureaus for a payment i made on time with receipts and I genuinely don not know what the next step is supposed to be. Has anyone actually resolved something like this and if so how long did it take