Hi Adz, welcome to the forum.
I am sorry that you have this bad experience.
The telephone number is from a third party company that is hired by Avast! for giving support. And they can charge you.
In my opinion Avast! doesn't make that clear ( enough ) on their website.
And from what we hear from users on the forum, the third party support company always tries to charge you.
My advise is not to call them !
If you want you can email a complaint to Vojta Nekvapil - nekvapil[at]avast[dot]com (3rd Party Support Manager).
But can you describe your problem(s) ? Than we will try to help you
Greetz, Red.