van der Wateren No. 5, commercial used envelope

Very rare commercial used envelope from Butwal to Birgunj,
adressed to: “Nepal cigaret Factory limited, Birgunj Nepal”
Postmark Butwal Hulak (post office) (Shrestha O 27), dated 2017 / Baisakh / ... BS = April-May, 1960 AD
With incorrect additional 3 x 2 Paisa. The rate became 10 Paisa in the mid of 1959