If you've only had your phone number for 3 years, it is entirely possible that someone else had an account at your drugstore chain using that phone number previously, or that someone goofed and entered an incorrect number, or that someone used a random phone number.

In any event, just don't save a payment method on the account and you will be fine. And you are racking up those extra points! Perhaps by 2025 you will have accumulated enough points to get a free candy bar!