You can try getting a prepaid SIM and using that number as a form of verification. I'd also keep trying to use online SMS numbers since even though they may not work in the first try, you can be lucky and find one working just fine.
I don't see anything wrong with what they said. Are only positive comments allowed? I don't think so.
I get that Discord (and others) verification can be annoying, but those measures are there for a reason. Too many bad actors trying to spam, etc. I wish we could go back to the early 2000s when we had none of this sh**, but more and more people are trying their hardest to ruin all the good things for everyone else, so here we are.