your letter
I still haven't received your letter.
I want to reply to your letter.
Thank you for your letter.
Cuando llegué a casa, encontré tu carta esperándome.
When I got home, I found your letter waiting for me.
Perdóname por haber abierto tu carta por error.
Forgive me for opening your letter by mistake.
Nadie puede entender tu carta.
Nobody can understand your letter.
Siento no haber contestado tu carta antes.
I'm sorry I didn't reply to your letter sooner.