Check the 'Messages' tab in account management and you should see a message confirming the purchase. It will say exactly what was bought.
If you cannot see a message in your 'Messages' tab it means, either, the purchase went to another account or the purchase didn't happen.
In that case, check your email for an email confirming the purchase. The email should say the display name of the account and exactly what was bought.
If you cannot see a message on the account or find an email, contact PayPal. If you can see a message about the purchase and everything looks correct, contact Jagex. To contact Jagex, go to the Common PayPal Issues support page and click on the last hyperlink
"we may be able to help."
There is a contact link to PayPal on that page as well.