How to deal with brokers blowing past LOI deadlines

Hi All, I'm looking for advice on how to deal with brokers that blow past and don't respect LOI deadlines. This is the second LOI I've dealt with this issue. On the first, we ended up backing out of the deal, which wasn't easy. Now, it's happened again with a separate broker. The broker has blown past the first deadline (requested an extension which we granted) and then also blew past the extension. We have been communicating all the while, but it's clear that the brokers are shopping the deals. Not sure how to continue dealing with these situations. I would appreciate any thought and advice people have.