Brackets on Nhs braces keep coming off

[vivicate]

My 14 yr old has had fixed braces with wires on for 3 months now, but since 3 days after 1st fitting brackets keep popping off for no reason, 1st time it was 3 when brushing teeth, then another 2 couple of weeks later then another in the night and another while sat watching tv and most recently 1 while brushing teeth and 2 more at front hanging loose, each time we go back the orthodontist swears my son is doing stuff he shouldn't and says he has never seen this problem before, this last time he gave me a lecture and basically said my son was not being truthful and if any more come off he is withdrawing treatment and we will not be able to get any more on nhs elsewhere, my son has followed all the guidelines, sometimes being overly careful because he is worried, now I don't know what to do.