I've ran into issues with that faction before, they tried to pull the same trick on Pariahfolk.

 

I told them there and then their deal was null and void because they signed it based off a misinterpretation of a rule.

 

Continue to wage war and raid, and screenshot when they make any sort of statement involving a ban or punishment. Falsely claiming such things is not allowed.

 

 

 

Remember people, unless those you raid ask for terms of surrender, you can continue raiding untill your heart's content.