The purchase included the ability to update to 10.0, without making the purchase you would not have been able to update to 10, so that is one update and that is why you made the purchase, not for unspecified updates that may or may not have occurred.
When you buy a version period, that gives you access to all versions already released and future versions for a particular time period, but there is no minimum (or maxmimum) amount defined.
If you had purchased a 2 year period would you still be complaining ?
If I had released 10 new versions in that time period would you be telling me I had released too many updates and that you wanted to pay twice ?
I could have said £10 to upgrade to 10.0, and not offered any update period and I suspect you would have still purchased last year. I could have said £10 for 10.0 and minor version updates as many software vendors do (e.g JRiver), but what constitutes a minor version is totally arbitrary, so my view was much fairer to base on a time period so yo know there will be no additional payment whatever releases are released for that time period.
Accusing me of fraud is frankly ridicolous, and I dont think any court in the land would back up that claim. I am kind of tired of working my hardest to provide great products, and then having to deal with an accusation such as this.