You can only do one WSNM quest at a time. However, you can cancel it by talking to the NPC that gave you the quest
This is the quest and people say you can cancel them but I can't. It shows up under Bastok Mission Inheritance (Ground Strike Quest) and I have even gone as far of completing almost every quest in the zone.

Talking to Gumbah doesn't yield any options. Maybe because I've finished Voracious Resurgence which he was apart of... Either way I'm stuck. I think it is just bugged for me.