Revert to KM10

First off, I just paid 2 months ago for an upgrade. Now there's another one. Feel totally jipped at this point getting nickel and dimed.

Business models aside, when I click on "Use Existing License" it tells me my license is invalid bc I have KB11 but my license is on v10. So how do I go back to 10?

Email Stairways Software at to quickly sort out licensing issues.