One should still not be charged for roam in PR.
There advertisement says PR is in network
If you get billed for roaming charges while on PR you are a short customer service call away from it being fixed.

In St John we lock on to the BVI towers and have been charged for roaming. When we get back, I call AT&T and they say "No Problem Mon" and eliminate the charge.

Hope it works out for them.

“Every time I open a bottle of wine, it is an amazing trip somewhere!” José Andrés