We appreciate you reaching out to us through the Xfinity forum. I would be more than glad to assist you with troubleshooting this. Do you know who the manufacturer is for the signal booster? A brief search online rendered several signal booster makers for cars. Let me know who made your signal booster and what kind of phone you have and we can take it from there.
I read last year that Xfinity Mobile does not officially support (or register) cell phone signal boosters. Is that still the case or have they changed their policy on registering and supporting cellular signal boosters? Thanks.