Ok got another bag. Replaced this morning.this is the bag I took off. Also had to use a crow bar to get top plate out!
Only thing to say is that the bag, if in good condition when you got it, folded over the bottom plate, must have been fitted incorrectly in the first place. If you received the bags in the full extended position then fitting them is a whole different ball game. You need to carefully get them to fold or they will not expand nor contract in a linear fashion but just go sideways and pop off the top mount. Which i think is the case with the one shown.