Questions: Break Up & Divorce

For reference, we were together 2 years, we broke up last August, we haven't spoken in 4 months (we agreed on no contact for a few months), and he's convinced that we're getting back together even though I told him I'm not interested. He's very "persistent" (read: doesn't take my 'no' for an answer) and it actually took me about 4 attempts to finally manage to leave him.

Anyway, I got flowers delivered to my house on Valentine's Day, with no tag. I figured they were from my ex, since I couldn't think of any other reason they wouldn't have a note or tag on them... I am seeing someone else currently, but he doesn't know my address, so I knew they weren't from him. Anyway, I called the florist yesterday and they confirmed that my ex ordered the flowers.

So what do I do? Both my parents said I should text him "thanks" because it's the proper thing to do or whatever. And I do feel guilty that he spent money on that. But all my friends say (and I agree) that it took me enough effort to get distance from him, so opening up contact with him would just open up a door that took forever for me to close. Any time I show him kindness or politeness, it just takes even longer to shake him. All he cares about is what he wants. Doesn't matter that I've made it clear I don't want to get back together. If I text him "thanks," I just know he'll take it the wrong way.

Tl;Dr: Clingy ex sent me flowers in an attempt to get me to talk to him because he wants me back and won't take "no" for an answer.