Wow, your "ex" definitely is the person who lost the most when you two ended your relationship. I say this because if you are seeking to fund the vaccination of their entire family, you obviously have a heart of gold, . 👍💛
Here's an example of the current situation in Phuket. You said that you weren't planning on visiting TL until July, so hopfully by then the situation will be much better.
I recommend you postpone until the late fall. Right now everything is closed and only about 1% of the population is vaccinated. Vaccinations should be ramping up this summer. Maybe by late fall, early winter (high season) Thailand will be coming out of hibernation.
looking at the upgrade page of the app, it does say "keep your number when inactive" when you choose to subscribe. Maybe you were inactive for too long and that is why your number expired?
Try this. I've been using it for a few years now. They give you a free US number so you can call any US number free and better yet people in the US can call you free anywhere in the world and you can also text SMS style back and forth for free from anywhere in the world. If your great grandmother lives in the US and still uses a landline, she can literally pick up her phone and call your US number and it will ring on your mobile phone (regardless if you are in Thailand or Peru) as long as you have internet access. It's ad supported but I've never found them to be annoyingly intrusive. You can pay $10 a month to get rid of the ads but I just stick with the ad version. Also works great for OTP / 2FA with your US banks etc. I also have Magick Jack (I've had it for over 10 years) but I always end up going to this app because the call quality is typically much better. Good luck!!