First, be sure you see the good application on the Market: Pure calendar widget is different of Pure GRID calendar widget (see here).
If you don’t see Pure calendar widget, you should read this.
If you see it, but the Market ask you to pay again, this is because the Market need some time to receive informations about purchased you already made. Generally less than 24h. So, you just need to wait.
If it still doesn’t work, you need to contact Google. Developpers can’t do anything about this.
Also, be sure you didn’t change your Google account because it is not possible to transfer purchases from one account to another.