deleting a gateway in Cyberoam

Our ISP changed, and suddenly I had to delete a gateway on the Cyberoam which was no longer active. With the gateway still existing, the device was unstable and not allowing incoming connections. First took a backup as P advised, System -> Manage Data -> Backup Data. Then, going directly to System -> Gateway -> Manage Gateways and trying to delete it gave the error message

Gateway used for pool(s) or Acting as Effective Gatway or assigned to firewall
rule cannot be deleted

(sic)
So I went to Firewall -> Manage Firewall and removed all the firewall rules relating to virtual hosts which mentioned that gateway. Still no dice. Then removed those virtual hosts too. Still no. Then removed the relevant host names from Firewall -> Host -> Manage. Still no. Then, during a support chat with Tech support, thought about other firewall rules, outgoing rules for eg. Lan to Wan and so on. Went through those, in a couple of them the old gateway was the Primary. Modified the rules suitably, then the gateway could be deleted.