I'm done booking stuff

Are you talking about offers in your email? If so, you can unsubscribe from each of the emails that should take you off their list. Otherwise you can just mark them as spam and they might slow down or stop. The best advice would be to have a separate email address for wedding stuff, but since you are already done it won't help you, but might help someone else.

You could just simply tell vendors that "thank you, but we've gone with another vendor"

If you mean the vendors on WW, have you marked them as either "hired" or "not a good fit?" My offers/messages on WW stopped after I marked a vendor as "not a good fit." I'm not sure if it notifies them when you do that, but I haven't gotten anything from them since doing that.