Changing my contract without my consent or notifying me

Vox changed my upload speed from 50 to 10Mb without notifying or consulting me. Logged a complaint only for someone to call me back 4 months later. The person then went on to state they never had a 50Mb upload option and sent me a modified unsigned contract to show this. I have all the email backups and originally accepted contract and invoices that state 50Mb upload. This is amounts to ***** on their part.