I am sorry to hear about your bad experience.

I, for one, can also confirm that CEX.io have always been good, I haven't used them a lot, I must confess.

But up until a month a go or so I was using it now and again and never had a problem.

I suggest you insist with all possible channels of contact before you then involve the authorities against them, there must be a reason although I agree such delay is unacceptable and unprofessional.