Ash here from the Shopify team. Welcome to the Shopify Community!
I'm happy to help out with the issues you're facing. Could you please reply back here and share some screenshots of the text messages and authorization codes you're receiving? This should help me identify where they're coming from, and determine how we can prevent them going forward. Since I'm not entirely sure what these messages and codes are for at this time, before you send the screenshots over please be sure to cover or blur out any sensitive information that may be in them.
Looking forward to hearing back and taking a closer look into this with you!