"It's just offline conversion events being uploaded so you'd stop getting these ads, or so they can market to you again in the future. You purchased this product, gave them a phone number.. Not sure where the issue lies? You agreed to the terms on Spreadshirt which is probably where you opted for marketing."
This is the basic approach. You give it to us. You agree to whatever we put in legalese and now we can do whatever we want. What?
It is disheartening, but I agree with the rest of the posts on HN that it is not at all surprising.
I just don't know how to approach it.