First thing you should do is join the Follow Up Boss Community group on Facebook. It's a great resource for people using FUB, you will find a link to it in our real estate community groups blog post.
First the issue is that you are most likely using your FUB # as a cold prospecting phone number. You need to stop doing this. Your FUB # should primarily be used to communicate with people that are willing to communicate with you.
You can refer to this article about cold prospecting with FUB on your options there.
Second, what you need to do is register your # with the free call registry.
If that doesn't help, you need to get a new number from FUB and this time don't use that # for cold prospecting. Don't forget to register that # as well.