Maybe, the worker might have forgotten.
I bet he didn't had any intentions cheating you.
The worker would be serving 100 customers a day, so it's normal for him to be abit clumsy at times.
It's definately not his fault.
I think you should gone to the Boss of the shop to clarify things, Instead of being disappointed or feel cheated.
I've also change alot of Currencies during this last 5years as i've been travelling.
The people i change with are usually Indians,
so please don't be racist. don't portray them as Bad people, for a small issue.
[ GIVE RESPECT & TAKE RESPECT ]
I respect every Races and Religion, so stop calling those People with Nicknames.
It's very rude. As Singaporeans, we are taught not to do such stuffs.
I hope you all would understand.
As for erection2011, I think you should go and clarify with them.
In my own experiance, i've changed currencies with the Moneychanger whom you're referring to.
They never Dissappointed me so far.
They have given me good rates and good service.
I think you should Go back to the shop and clarify with the Boss.
I bet with you 100 percent, you'll get your $20 back.
They won't do it Purposely. As for Money changers, 20 dollars is nothing to them. (not necessary for puasa money)
So don't worry! You'll get your 20dollar back!
and later on, i bet with you again you'll remove this post and write something Positively!
Cheers! XD!