Green’s Dictionary of Slang

dong n.2

also donger
[echoic]

1. a blow, esp. with the fist [post-1930s use is mainly Aus.].

[Aus]Baker Popular Dict. Aus. Sl. 24: Dong, a blow, esp. with the fist.
[NZ](con. 1940s) N. Hilliard Power of Joy 223: ‘Ten dongs!’ [...] The usual punishment was six dongs but this was a serious case.
[Aus]Teleg. (Brisbane) 5 July 8: Dong, poke (punch) [OED].

2. a phonecall, a ring.

[UK]‘Q’ Deadmeat 118: I’ll give him a dong on his moby.