I found the number in google search is a correct number for support?
That number isn’t correct/current as far as I’m aware - The number is on the avast website http://www.avast.com/support.
The free 24/7 support is provided by a 3rd party support service and it is limited in what they support - there is a likelihood they will try to sell support services if it isn’t covered.
Personally I would ask for assistance in these forums.
Yes I agree with DavidR that Assistance here on the Forum is the only way to go and it’s Free.
Also a simple Google Search for “avast support phone number” will come up showing a dozen or more ‘different’ numbers consisting of 1 800 and 1 855 numbers for various locations around the world.
None of which I’ve ever tried 
Well, i called them and they helped free of charge.
That is the general idea, if what you seek help for is covered - otherwise they will try to get you to sign up to an annual support deal.
You only have to browse these forums to see many such attempts to have the user purchase a support package.