Hi Rock,
Don't tell them that you want to cancle it. Just ask them that you are waiting from last 4 months. If they can't process it in next 10 days, then please return it. Be polite, may be you have to apply again in future.
I know some of my friends got visa after 5 months

If they took that long then it is sure they will give you visa, otherwise they don't keep application that long.
best of luck !