iMessage and Facetime constantly "waiting for activation"

I've been travelling abroad in New Zealand for about 2 weeks now. In preparation for this, I switched over to Google Fi back in January to take advantage of their "unlimited text and data abroad" plan. For the first two weeks things were fine, but 2 days ago I was suddenly unable to send iMessages. I checked my iMessage and Facetime settings and found the apps stuck on "waiting for activation". I was told to wait for 24 hours to see if it would fix itself, but after that time elapsed the problem hadn't been solved. I troubleshooted the issue online and tried everything recommended: checking for updates to the iOS (there weren't any), turning the apps on and off, restarting my phone, signing in and out of my Apple ID, erasing and re-entering my country code. No matter what I try, I'm still not able to send or receive iMessages with my phone number.

It's worth noting that I can now send iMessages with my email, but I am unsure if this has always been the case for my 2 weeks in New Zealand so far or if this is a new development.

Incase it is significant, I have an iPhone 5S. Any help or advice would be much appreciated.