Could you please start sending the letters by tracked mail, obviously I’ll pay the extra?

We have no control if the mail is slower than normal, that is clearly out of our control. What you are asking for is not within the abilities of the business. We mail thousands of letters and postcards per day. Sending someone to the post office to get tracking on your letters would require too much time - for what we'd have to charge, not sure it's going to be worth it.