Unable to downgrade mobile plan

I switched my Xfinity Mobile plan from Unlimited to Premium Unlimited back in October because I needed the 5G hotspot while I was out of town for a week. I've called every month since then to downgrade my  plan back to Unlimited. Support tells me it's been taken care of and will be reflected on my monthly renewal date. For whatever reason, it never downgrades and then I have to call for a credit. I've spent probably 10 hours on the phone with support trying to resolve this. I am on my way out the door. This is my last attempt.  Why cannot you not switch this back?