I want to fix a cabinet to a bathroom wall. The wall is 710mm wide and has a single stud slightly off-centre, about 270mm from the right, but which is too near the middle to be useful for hanging the cupboard.
I was planning to use heavyweight plasterboard fixings. (I think they're also called mollies.) The pack I have says "Interset(R) 10mm Plasterboard Fixing... DRILL DIA: 10mm, FIXTURE: Max 15mm thick".
Unfortunately, when I drilled into the plasterboard, it turned out to be much thicker than I expected. I used a paperclip through the hole to help measure the thickness, and it turned out to be about 32mm thick. This seems to be much thicker than is common for plasterboard. Now I have a pair of 10mm holes in this plasterboard and I'm not sure what to do with them. I'm not sure if it's normal plasterboard, or something else. I thought perhaps it's insulated or sound-dampening.
For context, the wall in question is internal and divides one apartment from another. I understand it must have been installed in the last 10 years, since the apartment was formerly a ground-and-basement-level shop, and was converted into apartments within that time. This is in the UK.
What can I use to fix a cabinet to this thick wall? Can I get spring toggle bolts that are suitable for this thickness? How do I find suitable fixtures, since most seem to be designed for 10-15mm walls?