What kind of car did Hagerty think it was?
When I first insured my car, the lady I talked to asked "what is it a replica of?" I tried to explain that it wasn't a replica, but she said it MUST to be. So, I told them it was bit like a 1967 Lotus Super 7, which another forum member had used in the past to get their car insured. I then promptly explained that's NOT what the car actually is, but it's the closest thing I could come up with (open wheel, open cockpit, roll cage, etc).
That worked fine. The VIN matches my car on the paperwork. No issues with Hagerty yet.
I would simply call them back and talk to someone else. I really think it's 90% who answers the phone. The gal I talked to didn't seem to care about much, and was happy to help any way she could.