Fortunately, regulation seems to help at least a little bit, but you kinda have to be prepared to wage some war - or eat your losses.
(Just lost a phone number that has been my primary for over 7 years; that's after losing another one that I held on to for 11 years... Not to mention all the smaller stuff, like how contracts/extra packages are structured once you go over the month's limit.)
The one I use literally just increases how much data is included with my plan, rather than increasing the price. I quite like it. (I don't think it's available outside of austria though)
As such, I am never going to switch to Telegram or Signal unless you let me have an account that's not tied to a number. I've lost shit in the past because of this, a phone number is only a temporary identifier.
Regulation = high barrier to entry in industry = monopoly/oligopoly = all telecoms are bastards.