So you sign up on website.com, you click on the notorious I accept tos and privacy policy checkbox (many without reading it) and you pay for the service.
Month later, website changes their TOS page adding few new paragraphs without notifying you that allow them to bill you $10 every month.
When you complain, they say: Read our TOS, you agreed.
How can you prove and show the original TOS changed? That you never agreed to this version of tos at all?