Fake Xbox Account Phone Verification Numbers?

I've been selling a lot of Xbox services that require me to make a lot of accounts. Simple enough. Hop on a VPN, use an unlimited gmail account generator and sign up for Xbox until I've made like 10 on that IP, switch to a different IP, repeat. Problem is, after 2 days they all get locked. They require me to submit a phone number and obviously me & my friends are damn well past the number of times we can use ours. This is fine for now, because I can make so many more so easily, but it takes good 30 minutes for this. I can ver easily imagine this process becoming really fucking annoying every day. I've tried websites like https://getfreesmsnumber.com/free-receive-sms-from-us but it always says "can not send a message to this number." Guess Microsoft is smarter than I thought. I know I'm allowed to submit numbers because I'v been using my regular friends' numbers for a while w/ these, I think they can just suspect fake SMS bot numbers. Any ideas boys?