The highest response rates we’ve gotten happen when we’re NOT super annoying and we make it easy for someone to respond.
Short and sweet, along with persistent checking in, will help you more than a long diatribe. This is a great time to be using FollowUp.cc to ensure that you don't forget to follow up. It’s important to try and find out why they aren’t responding, what their core problems actually are (sadly, you may not be helping with that), or why they don’t like you.