Ah, thanks for the photos. That is indeed what I ended up doing. It’s not what I’ve been used to with Nokia phones, so I was trying to fit the SIM into the clip - see here a typical one on a Nokia N900:
You see that the SIM (a larger ‘mini’ in this case) fits into the metal clip and then the clip is closed with the SIM in the clip…and the clip pushed forward, similarly to how you describe.
So, that is where I went wrong. I had been trying to fit the SIM into the clip, when I should have just done what I ended up doing (which, tbh, didn’t seem especially secure), which is as in your photos. I imagine the fiddling I did to try to get the SIM into the clip quite possibly caused the clip to come off at the hinge.
Perhaps I should have read the user manual (I didn’t), though I see that it doesn’t help on this issue either.