Wait...your insurance agent is telling you that you'll pay for the REPAIR, or the DEDUCTIBLE?

Because if it's the former, you're getting screwed. I'd look into getting a lawyer, if the damage is bad. I'd definitely threaten to contact your state/country/whatever's insurance regulators, and Consumerist.com and whoever else covers stories like this.

If it's the latter, well, there it's more ambiguous.

If there was no damage to your attacker's bumper, he's lying. You shouldn't be paying for anything.

If there is, he might not be lying, it might not be the fault of anyone whose insurance is actually involved, and he shouldn't be paying your deductible.

Regardless, the insurance company could just be trying to weasel out of it.