@psssammy Is it just calls? If data and texting work it suggests your phone may not be VoLTE capable or "certified". The list of approved phones is here
https://www.publicmobile.ca/en/on/get-help/articles/volte
If nothing is working, make sure to try 4G/LTE on each of AT&T, T-Mobile and Verizon. If data is not working make sure data roaming is turned on in settings.
Phones must be VoLTE enabled to work in the USA since they shut down their 3G networks in 2022. If that's the problem you could try connecting to T-Mobile's 2G network which still exists in some areas for now.
Edited to add the obvious question, you do have a Canada-US, Canada-US-Mexico plan, or a US roaming add on?
