Report them to the police.
In April, I had offensive texts which eventually morphed onto threatening texts off a would-be client. I took the bait, eventually replying with a text that wasn't very polite, a few more in the same vein, (suggesting that he needed mental help) then one threatening to report him to the police if he didn't stop. I blocked his number off my phone, he re-acted by changing his number.
About month ago, I received a phone call off suffolk police, informing me a complaint had been entered against me for 'mis-use of a mobile phone' or some such nonsense; yes he had filed a complaint against me!
When I explained that 'he started it!' They said I should've reported it at the time...
I had to go and sign a piece of paper, stating 'I was sorry'.
Also they let his name 'slip' to me; so did they let my name 'slip' to him?
Didn't mean to go off on a tangent, but yeah, I would just log a complaint and make a note of the crime number.