Cellphone not receiving texts

Factual Questions
1

Signing up for a Bitcoin exchange requires authentification which is usually done by sending a text to the phone number you provide and then using the content of that text as verification. I used to be able to get them on my Nokia C1 but that doesn’t appear to be the case anymore. My phone contract hasn’t changed as far as I’m aware.
What could be causing that problem?

Are there alternatives to providing a phone number when signing up for Bitcoin exchanges?

2

SMS is pretty reliable but not perfect. Messages may never be received, delayed by hours, garbled, etc. Information sent in SMS is not secure, but it may be reasonable to use in 2FA.

Call your service provider to ask them.

3

I would GIVE a bitcoin for that lack of functionality - not a fan of texting, me.