Identify a non-Lego Santa set
I could not find anything for 'Santa's letters' and the parts with 'North Pole' where showing different stickers on Bricklink,
Based on the design of the bricks and the strange colour used for the characters I strongly suspect these are not LEGO bricks.
The 2x2 slope for example does not show a visible LEGO logo on the studs and each stud is quite different. The bags they are packaged in are also not standard.

It will be quite difficult to identify this set if you cannot find a box, instructions or some other markings/part numbers. Clone-brands rarely have an online set database where you can find sets or an official website.