What to do when a 6 year old says 'No'!

[SingleMum01]

Always been very amenable, now started to say 'no' to things he's asked to do. Counting helps, but still drags his feet. Is he just testing boundaries?

Also puts fingers in ears and says 'la,la,la' when I tell him off. Which he knows I find unacceptable.

Advise please

I become Boris Johnson

I laugh and wave my hands nonchalantly and say "oh no, i can't be bothered with no i'm far too busy, get on with it" and walk out the door shaking my head.

Sometimes it works....