What captcha more are you using? ReCaptcha? Internal? Captcha is in any way a guarantee. There is no way to guarantee you don't get bot registrations. It certainly helps, but doesn't eliminate them. Especially if your site becomes targeted for whatever reason as they can design their bot for your captcha.
I also have a problem when fixing a telephone format. Then no one can create their account even when they respect model.
You'll need to be more specific regarding this issue. Please open a separate topic though as it doesn't relate to this one.