It does not normally make sense to forward from A to B and also from B to A. That creates a loop, which results in an error. Possibly Vonage is ringing your Network Availability number, or Google rings your cell, after detecting the loop.
If you have a phone connected to the OBi (but not the Vonage adapter), forward your Vonage calls to GV, but do not have GV ring your Vonage number.
If you have a phone connected to the Vonage adapter (but not the OBi), have GV ring the Vonage number, but turn off forwarding at Vonage.
If you have separate phones connected to both devices, you probably don't need either forward.
If you have canceled your Vonage service (as opposed to porting the number), then when it is disconnected you won't be able to receive calls on your Vonage number anymore. Callers may hear a message that the number has been disconnected, or (if you have arranged this with Vonage), they may hear a message advising them of your new number.