Yes it is totally unacceptable and you shouldn't have to pay anything.
Assuming this was the telephone number on the avast website for support, this is provided by a 3rd party:
The third-party Support Manager, has requested info about 3rd party support issues, so if you have time to recount your experience (copy and paste your post, and see the above post link, etc.), give the link to this topic.
Vojta - 3rd Party support Manager - Vojta, nekvapil(at)avast(dot)com