OP needs to provide more information. What was the aircraft size & how much of a delay was occasioned by the bump?
This was an IDB because OP was removed from the flight without his agreement. But, depending on the size of the aircraft and the length of delay occasioned by the bump, the compensation due could be anywhere from $0 to $1,300 (paid in cash).
If the IDB would have been $0, the GA did OP a favor by turning this into a VDB (which it wasn't).
For what it's worth, the "V" means "voluntary." There is no fixed amount and it is whatever you agree to. It is generally paid in the form of vouchers, not in cash (check) and can also include other incentives such as a hotel, food, UG's and the like.