Sounds a bit iffy to me. Contact Dollar and ask them for proof of the violation, as they will be able to give you photographic evidence of the violation.
As you say, normal practice is that Dollar simply debit your card with the relevant charge and then tell you they have done it.
I found something similar here
if you want to have a look.
The correct contact details for Dollar are
Dollar Rent A Car, Inc.
Attn: Customer Service 2W2
P.O. Box 33167
Tulsa, OK 74153-1167
Toll-free Support Service: 1-800-800-5252
Although the address is similar, it is not quite the same and looks like a phishing scam to me.