I hate to ask such a simple question but I do not know exactly how much of a noob you are (or are not).

If you go to the "Receive Money" tab in your blockchain.info wallet how many addresses are listed under each of the sub tabs "Active", "Archived" and "Shared"

Make sure you go through all three and see if either of the addresses in question are listed there (especially the change address)

Now more interesting questions:

Do you have any remaining balance in your wallet or did they take everything from all addresses in that wallet?
Are you using the web site directly or using a plug in (plug in is a bit safer)?
Are you using two factor authentication?
Are you using the web site only, android application only or a combination of the two?
Do you have any other wallets besides your blockchain.info wallet?
Do you use the password you use at blockchain.info at any other web site anywhere?