First off try isolating the problem by using another VM and see if it can reach the gateway. Can the network team make the gateway pingable (and routeable) from another network while troubleshooting?
Try troubleshooting this using a top down method.
First make sure the VM has the network card connected (marked connected) in its settings page.
Then make sure the OS is NOT configured for VLAN tagging.
Check the Portgroup the vmnic is configured for. Does it have the correct VLAN?
The ports of the physical switches, are they configured as a vLAG or an mLAG (do they share MAC address information). Do they have the correct VLAN trunking configured for the port it self. Is the MTU size consistent? How is the network configured? Does it use STP? Is the physical port on the switch configured for RSTP or as a end device (terminology differs).
Hope this helps.