Anything made out of pressboard does not last long and is difficult to repair.
Ah, I wouldn't give up on it just yet. In building R/C airplanes I had to learn a bunch of repair/fabrication/finishing skills. One thing to try would be mix up a batch of slow-curing epoxy with microballons (tiny glass balls, it looks like dust) as a filler material. Chopped fiberglass is stronger, but is hazardous if you breathe it so a dust mask is required when working with it. For the cabinets, instead of epoxy one could use wood glue but it won't be as strong. Sand it down smooth when the glue sets and if done right the repair is invisible under a coat of paint. Using a sanding block is essential to get the edges feathered in correctly.
I used that technique to repair a partially rotted window sill and it still didn't show ten years later.
Any hobby shop worthy of the name will have those materials.