Someone keeps trying to sign into my icloud account

I've started receiving apple verification texts on my phone constantly (It's not a scam number). I have 2-factor authentication turned on and once it happened a third time I changed my password to a very long and complicated one, with random letters and numbers, and logged all my accounts out. I thought that would be the end of it but I've just received two more texts with new codes, and I'm receiving texts from the spam number '51472' with fake apple verification codes too. How do I get them to stop it because it's incredibly annoying and I've already changed my password but yet I'm still getting texts?