nissan micra airbag light fiasco?

My nissan micra's airbag light is flashing for the third time in its 5 year life. the first two times i has it fixed at evesham's nissan dealership, this time we took it to a different local nissan dealership. they charged £300 for a service today but did not switch off the light. Now they want £250 to fix the airbag light and say the door has to come off to do this? can this be right?
If I follow the key trick of resetting the light and then WD40 the connectors will this mean the airBAGS ARE NO LONGER DISABLED?