I checked into Ooma, it should work.
Configuration issue?
What is the specific complaint your customers have?
Also, have you talked with your Internet/Gateway provider?
They don’t like my phone number. They call it a ‘verification’ issue. I had to call them up and explain, yes, this is my phone number; it has been for over ten years, and it’s the only one I use for business; and yes, it’s the number attached to my bank account.
(I haven’t talked to Internet provider because if that were a problem, it wouldn’t be happening with only two companies and not with any of the others. I can only assume they don’t like my phone number because they can’t automatically verify it, as they can apparently do with other, bigger telecom companies.)