Rear seatbelt guide - a small problem, but annoying

Quite early on in my ownership of this 2016 Combi one of the plastic plates (drivers side), which takes the wear and tear of the seat belt sliding over the back rest of the rear seat, came off.

It seems to clip into two holes in the metal below the foam padding under the leather and does not appear to be broken - there are no rough edges showing.

I have tried many ways to get it to stay in place without success - squeezing into the metal holes - just pops off again, glueing with hot glue gun - lasts a couple of weeks, sticking with double sided tape - same result as hot glue.

I hate it when passengers tell me that a piece has fallen off the car, so I would really like to fix it once and for all.

Any of you experienced Superb owners had this problem and found how it is supposed to be attached?

(I don't want to pull the other one off to see how it is meant to go, in case I end up with two that I can't fix!)