What can i do to download the theme?
There is nothing you can do to download it. The transaction information passed between paypal and boonex after the purchase was made must have not completed properly.
The only way you will see a download button for it now is if the developer manually processes the transaction so the purchase will show up.
You have two options at this time.
1) Contact the developer again.
2) Issue charge back through paypal to get your money back.
If the developer does not respond, don't wait to long. You only have a certain amount of time to issue charge backs through paypal. I would not wait any longer than 1-2 weeks.