How to say NO to your friends?

Lately, I got many fone calls from an old friend and apparently she was not calling me for concern, but trying to sell her business, insurance. She keeps calling me these days and I politely refused her and told her I have been busy these days. I told her if I need any insurance consulting or contracts, I definitely will let her know but now I do not have this kind of issues. However, she does not buy it and keep contacting me. She even calls and sms me three or four times a day and emphasizes how good her insurance contracts are. So I think I have to think a way to say NO.

Now I am pissed and think she is so annoyed. The first step to say no to her is refusing her fone calls. But I am afraid that our classmates’ reunion is coming soon, and if we meet up there, that will be very embarrassing. So what is the best way to say no to her? Just tell me!