The way you deal with Flock and their cameras is that you tell them you are terminating your contract with them and will be remitting payment for the remainder of the contract term. They have 30 days to remove the cameras from your property or arrange for removal. If the cameras aren't removed, you will remove them and store them at Flock's expense until Flock comes to pick them up or makes arrangements for pick-up.
Then you send them their money and, if the cameras are still there after 30 days, take 'em down and put them in storage. The cameras may belong to Flock, but it's still your property they're mounted on and Flock no longer has any right to have their stuff on your property. Don't argue with them, don't get into a debate with them, just do as you said you'd do. Sure they could take you to court, but seeing as they've received all the money they'd've been entitled to and their property is sitting there nice and undamaged waiting for them to come get it the court's going to ask why their case shouldn't be dismissed for failure to state a claim.