This is to be expected. First the ramming and then denial of responsibility. Was there any video of the incident? Or pictures of the approach? 
I would report the incident first to the Coast Guard as and accident (Collision) report with extenuating circumstances leading to the ramming by the police boat. In future record all communications on a recorder and have video cams always running when needed.
It is obvious that the Police vessel made a very bad decision resulting in damages. They should be held to account either monetarily and a public admission of responsibility in this breach of maritime regulation on the river. 
What were they thinking? Would be interesting to know. I see the rebuttal make little sense given the situation. I would push it. Make them apologist and pay for the damages. As long as it doesn't interfere with the scheduled. 
Someone out there may have a video of this. Try to find them.