How do I get my Money back?

I bought it yesterday and want rid.
This is a very unreliable product, nearly caused me to have to rebuild my PC as it crashed Avast and would not let me back into my system. Had to go into safe mode and remove AVAST with avastclear.exe (after searching Google on another PC) Then reload AVST
Even then it still looped around with a system dialogue box (switch, retry, cancel)
Eventually connected once but now wont connect and says it has a technical issue and that it expired -16502 days ago (I only bought it yesterday)
I am angry and frustrated and want my money back.