Question for LENTSWELETAU SUB LAND BOARD

Helo,i have changed my postal address from Private bag 0095 Gaborone to P O Box ******** Gaborone.I wrote a letter and send it through post office.I did not see any reply I do not know weather I was not suppose to send it or I have to bring the letter in person.How will I know you have seen my letter?thank you in advance