Very first thing I’d try would be using Cambium’s collocation tools to see if sync can provide relief. We were in a similar situation and were about to either abandon 3GHz or try Tarana when we finally decided to try sync and all of our issues went away. I wrote up a pretty detailed forum post on the experience along with sync recommendations HERE.
Another thing to check would be to make absolutely sure your PAL’s are actually in use and being recognized by the SAS. You can do this by contacting your SAS provider and auditing the sites in question with them to make sure your PAL’s are in order.
Next step would be to identify the other operator and then reach out to their spectrum compliance team and see if you can come to an understanding. If you wanted to take it a little further, you could employ the help of an FCC-seasoned attorney, like Steve Coran @ Lermen Senter, to write on your behalf a strongly worded letter to the offending operator. He can also advise you on the next steps needed to escalate the matter with the FCC if this operator is breaking the rules.
I hope these steps help you get things resolved. I know how frustrating this can be!