Active job

Repair Wall Hanging Sink Cabinet in Bathroom that has come away from the wall

The wall hanging sink cabinet in the bathroom has come away from the wall as my son sat on it (!). I've tried adding some extra brackets to it but it still isn't resting back flush with the wall. Not sure whether it needs completely replacing or just a fix that I don't know how to do. This is in a family bathroom and so fixing this asap is important.