Need a low cost US cell plan

Help. I ported my US number to Mint Mobile.
After 3 months they tell me my Samsung phones (S21 & A30) are incompatible with their systems outside of the US. Have been able to send and receive texts but zero calls via WiFi or international calling.
Oh, and they refuse to re-fund my 3 month pre-paid plan as they claim I had to cancel within 10 days of activation. (Still waiting on that activation)

I have Google Voice (thank God) as that works for another line but I can’t port my business line as Google voice has my business line associated with that number. (so, I would lose my existing personal line. Ugh.)

I only use WiFi calling so looking for an inexpensive carrier like Mint purported to be ($15/month).

I ported from T-Mobile (which Mint uses their network in US and in Ecuador) That was $65/month for WiFi calling. Anyone else having luck with a low-cost carrier that is compatible with Samsung phones?

Thanks in advance,

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