Since blockchain wallet is online there are many possible can be happen you might be infected or you might be phished.

That's why I stop using online wallet because we can't blame them if you contact them they will always say "that the issue is in our side not their side" and they already have reputation in Bitcoin industry.

Next time don't use their service to avoid loses.

Do you remember the address if where your coins are save?
Maybe we can check it on explorer if still has the balance and maybe it's just a bug? Because sometimes they have some bugs reporting it to their support will fix the issue by refreshing your account(Just like on Coinbase).