Phone number issue

I have ported my phone number from my old android phone to my new apple phone. My calls are working perfectly fine but texting is being weird. When I message my friend who is on an apple phone as well it works, but when I message my mum who is on an android phone it doesn’t. She will text me and my old phone will receive the message instead of my new one even though it no longer has a sim card in it.

I went to Currys to ask about this problem and the two workers that I talked to were baffled. One of them was the apple specialist and even he said that he had never seen anything like this before.

Also, to create this message I’ve had to make an account even though I already had one. I went to reset the password on the other even though I’m sure it was correct and I didn’t even get an email. This mobile network is really confusing me, please help.