No, addresses are not one time only... although it is not advised for privacy reasons, you can re-use addresses multiple times.

On your "Payments" screen, you should see the address that was generated when you did the "Request".

1. Is this definitely the address that your cloudmining service has?
2. Have you checked that address on a blockexplorer like www.blockchain.info? Does it show the payments being made by your cloud mining service and a non zero balance?