Ask HN: Trademark infringement for rejected / awaiting response trademark

I was wondering if anyone has any experience on dealing with trademark infringements, specifically if someone is sending them out against yourself / your company when that trademark has been rejected / awaiting response.

Currently, I run a side project that has been up for a year or so, and ranks pretty well on the Google for a certain term. It is one of several of similar sites that all use this trademark and when the site was created, there was no trademark. Recently, a competing service has applied for a trademark and claims to have been in business for longer than my service (which is true) but the trademark has a status of rejected / awaiting response. That being said, the competing service is sending out Trademark infringement letters to third party services I use and getting those services cancelled because of it.

I feel like these services should at least validate the Trademark before making a decision and I have sent responses back informing (and providing uspto links to the unapproved trademark) each service that it isn't trade marked yet.

What are my options? I am certainly not in a position to legally fight the trademark, but it really irks me that someone (who I didn't know existed, even while searching for competing services) is able to shut be down, even without a valid trademark.