I am a masonry contractor. I did a general contractor a favor by grinding and tuckpointing the interior of a commercial building he owns. I warned him of the amount of dust and debris it was going to cause and he still wanted me to do the work. We did not have a signed contract and I received no payment for my services. He was present during the work and the when the dust set off the fire alarms he still wanted to continue the work. When one of the tenants came to work on Monday morning (a gift shop on the first floor) they were furious because he gave them no warning of the construction. When he got the clean up bill it was over 10,000 so he submitted it to his insurance company. Now they (his insurance co.)is trying to come after me for 1/2 of the damages. They have sent me a collection letter and are threatening to sue. Am I liable if they have no proof, other than his word that I helped him? He thinks that since I have ins.it should be no big deal to claim it, but why should I?

Optional Information:
Illinois

Already Tried:
I have just ignored their requests for my ins. information and collection calls.