I reused a previous deposit address and the recipient claims the address was invalid I sent bitcoins to Sportsbook.ag, my Bitcoin wallet saved an address that I'd previously used to send Sportsbook.ag. The problem is my bitcoins never showed up in my account. I e-mailed sportsbook.ag, they told me that the address I used to deposit bitcoins was invalid and I had to contact my bitcoin wallet. From what I've seen the bitcoins aren't lost, they're somewhere, how do I get them?
If you've used this address before to deposit money to Sportsbook.ag, the address will still be under control of Sportsbook.ag. If they don't directly manage their Bitcoin deposits, their payment processor will still have received the payment in proxy. 

They may not have expected you to reuse that address, but they should be able to fix it on their end. Contact them again and clearly explain what has happened. Good luck.