UPD: BCH balances have been credited, Bitcoin Cash market is launched. More info here.
As you know, Bitcoin Cash hard fork successfully launched on August, 1st. As announced before, we are supporting the UAHF and are working hard to implement the respective changes to CEX.IO platform. Thus, CEX.IO team is currently busy with the calculation of BCH coins.
Soon you will be able to see your BCH balances on CEX.IO accounts.