My parents applied for permanent resident visa here in Buffalo. Their visitor visa needed to be renewed during the waiting period. I applied for the renewal and paid $150 application fee about three months ago. About one month ago they received their landing paper and became immigrants. Yesterday I received a letter from visitor visa renewal office stating that since my parents are already immigrants they will refund the $150 as the renewal for visitor visa is not necessary.

Hope this piece of information will help someone that is in the same situation.