I reused a previous deposit address and the recipient claims the address was invalid
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.