Offered one price - charged another

I trialed avast cleanup then as the 30 days approached I was offered renewal special for 2 years for A$54 only to find they took A$54 out and only gave me 1 year subscription. Trying to get hold of them to sort this out seems virtually impossible. Can anyone advise please?

https://www.avast.com/faq.php?article=AVKB24#artTitle (Orders and Renewals)

Thanks very much ;D

You’re welcome.