Curtain brackets aren't very sturdy: they peel off, break and only last as long as the adhesive.
They're very easy to repair or replace with this model, suitable for 2 mm x 16 mm pins.
Print them as shown, it's quicker and, above all, much stronger, as the stresses are in the direction of the printed thread. 
Then install 14x14 mm pads of double-sided tape on the inside.
The hanging length is designed for 15 mm PVC windows, so don't hesitate to ask if yours are different.
If you can salvage the pin from the old backing, put it back in place with a drop of glue. Otherwise, use blind model DA010.
Happy DIY