I got the same but asking for 341.25. The VAT liability lies with the trader not the consumer, you're not obliged to pay it - HMRC won't come chasing after you. Of course, then we're into the situation of cancelling users licenses to force them to pay the extra. I've been having a look through consumer rights and generally it concerns the difference between estimates and quotations. If somebody quotes a sum of money they should stick to it. If it's an estimate the price can change. As far as I can see the transaction nearly a month ago with Unity was final - not an estimate - and they should stick to it. The clerical error was there own but we are paying for it. The whole debacle is certainly not a great way to connect with your users. As you state, the Unity4 upgrade path was an expensive outlay for many of us that had to scrape together the money from somewhere, and then we get hit with this - through no fault of our own! They certainly don't have the legal high ground - this is all very embarassing for them and for us to see. Way to go Unity.