Canceled service - continued billing

I transferred / canceled service on 5/8/26

Xfinity did not cancel the service on their end correctly. I went into a physical location to address this issue on 6/5/26. He agreed this was a problem on Xfinitys end and refunded me the payment they took out without proration cost. Now I am getting an email saying that my final bill will be almost $300 due to my service being canceled on 6/5 when really everything was transferred over and canceled on 5/8. Please help.