I have not experienced this type of problem in 12 years using Nikon - including 9 months with a D7000. A minor but important issue to resolve is are you or is the retailer now dealing with Nikon? A greater difficulty is how did the shutter blades get bent? You said "They simply told the retailer that the shutter flaps were bent which implied that I must have bent/broke them when doing a sensor cleaning?". I do not know what Nikon implied but my understanding is 1/ shutter blades do not get bent during shutter operation unless there is first a breakage of a shutter part 2/ if the blades are bent it is possible this happened from an external source - and this this is only likely to happen on a DSLR when the mirror is up and the shutter is open. 3/ Nikon build in several safety features to prevent damage during a sensor clean due to premature closing shutter blades perhaps trapping a cleaning swab. Not following the procedures is possible - with risk of damage to the shutter. You mention the retailer showed you the shutter before sending it to Nikon - this seems to confirm the blades were bent before it was shipped to Nikon. The implication is Nikon think the blades were not bent by a mechanical shutter fault - and therefore not covered by the warranty. What is not clear is whether or not the shop accept Nikon's diagnosis. Nikon's diagnosis seems to be a shutter blade impact. The best way to escalate the issue is to upgrade your complaint, possible in writing, by name, to a Nikon service manager, or director of the shop.
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.