How do I stop fraudulent texts from Apple support, about a lost iPhone?

Unless you are following a thread in Apple Support Communities, Apple does not set out text to anyone.

Click and read here => Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

All you can do is block each one when they come in. They are not actually coming from Apple, so there is nothing Apple can do to stop them.

If these are SMS texts you can also forward them to your carrier so they can block those senders for everyone. Most carriers use short code 7726 (SPAM) as the short code to forward spam SMS texts so they can block the senders for you.