I'm having trouble folllowing.
Instawallet is a website that provides a hosted (shared) EWallet service. Your EWallet on Instawallet has a single, static Bitcoin address associated with it. When you use a service and send to that address, it will appear in Instawallet after the transaction confirms.
Do not lose your URL for your Instawallet, as that is the only way to access and spend the funds later.
Are you saying that some other service is not sending to that Bitcoin address associated with your Instawalet? (you can verify if that is happening through the blockchain, and a service that provides a view of the blockchain is Blockchain.info ).