Still waiting on payment

I had a baby via C-section in July 2023. I got pre-authorisation for a 3 day stay, but then I had infection and was told by the doctor that I had to stay another night in hospital. A few months later, I was told that the hospital now finds me liable to pay the extra day I stayed in the hospital because Momentum will not pay it. I spoke to Momentum to find that they would pay, but the hospital needed to update the amount of days that I stayed and this would need to be done by a hospital case worker. I was cc'd in on an email from Life Hospital to say that they had updated the number of days, so I thought it was all sorted. Got another email from the hospital a month later with the outstanding amount that they still expected me to pay. I phoned Momentum again and was told that the hospital hadn't updated the system on their side and if Momentum were then to pay, it would be considered *****. Fast forward to phoning the accounts department and Momentum multiple times and countless emails. The last time I phoned Momentum was on the 23rd of May and was told that they were re-processing the claim and would then pay the hospital. I just received another call from the hospital and it still hasn't been paid. It's been almost a year. I don't understand why this has still not been sorted out and I'm extremely disappointed, as before now, I have not had a problem with them.