How come that everything you do ends up being a problem?
Get some who knows what there doing to do the work
Removing the airbox on the 500 requires great care and finesse if the small breather hose attachment is not to be damaged. The safest way is to loosen the bolts and ease the airbox upwards so that it's just free of the intake and not restrained, and only then remove the small breather hose. Removing the hose with the airbox firmly in place puts extra stress on the all-too fragile pipe.
It's not necessarily the OP's fault; it was quite likely broken already.
The plastic pipe in question (the attachment point for the small breather hose) is notoriously fragile; many of these were broken by franchised dealers the first time the air filter was changed.
I've good news, and bad news.
The bad news is you can't buy the plastic pipe separately from Fiat; you can only buy a complete airbox, and it's a seriously silly price, so this is not a realistic option. You can also probably forget about a secondhand airbox from a breakers, as the overwhelming probability is that the pipe will already be broken on all of these.
The good news is that it's reasonably easy to fettle a better-than new fix by attaching a suitably sized threaded brass nipple to the airbox. You might need
to drill out the hole where the broken pipe used to be, and it's definitely worth aralditing in the replacement for good measure, but it should be a workaround that lasts the remaining life of the car.
