To replace my Mint Mobile plan, I signed up for a T-mobile pay as you go plan.
Prepaid Pay As You Go $3/Month Plan, $0.1/text/minute
https://usasimcard.com/products/esim-activation-t-mobile-prepaid-pay-as-you-go-3-month-plan-0-1-text-min
This company is actually a service to open the T-Mobile account. I bought the activation package a couple of hours ago, was sent an eSIM, and I activated the number by installing the eSIM which was sent to me automatically. The phone number was activated but I couldn't make any calls because I didn't have any money in my pay-as-you-go account. Any call I made went to T-Mobile service in the US. I had to wait for a while to get a vendor PIN from the service, which was necessary for the next step. I then opened a T-Mobile account on the web, entered my new US phone number, verified my email address, verified the Vendor PIN, and am now all set. Total time was about 2 hours and all was done from Thailand. Now I have a US T-Mobile number and the company that helped buy the eSIM is now out of the picture, ie, all my dealings are with T-Mobile.
In summary, it only took me a couple of hours to be up and running with a new US phone number. Next step is porting over my old Mint Mobile number to T-Mobile by calling Mint Mobile Customer service and getting a transfer PIN, then calling T-Mobile Customer service with my old info such as Mint phone number and transfer PIN.