You don’t have to share your number to get spam messages - I get weekly spam texts for “Susan” (not my name), which I never interact with but have been coming from random numbers for years.
Once your # is on a list, whether you put it there or not, it never leaves.
I’m the only one who has ever had this phone no., but if I were to swap now, 99% chance I’d get a reused number, which would probably come already loaded on a million different spam lists. There’s no winning.