This company is like a ghost. I have gone on every help page and can not find anything about cancelling during my 30 days, they don’t have a phone line? How do I get in touch with them before my 30 days are up?
→ https://www.avast.com/faq.php?article=AVKB24#artTitle (Orders and Renewals)
No ghosts here 
This is possibly the fastest reply I have seen in my time in the forums exactly 1 minute.
So you know where to come for a fast response to your question/s.
This company certainnly is like a ghost! When you follow the FAQ and the help/support trails - it still doesn’t help. Of course it is deliberate and I think I just got sucked in - big time!
You could start by asking for help and giving some details of exactly what it is you are having a problem with.