Do not buy CD Keys from CDKeyWorld or any other unauthorised key seller or off auction sites (eBay, etc).  In doing so you are throwing money down the drain because Steam more or less ban nearly every single one of these keys bought from such sites because they are unauthorised sellers. And based from what I've read in this thread and on other boards, these sites know the huge risk you are taking and the likely hood the key you buy from them will be banned and yet are extremely reluctant and difficult in providing you with a refund.

The reason the keys get banned is because the keys are bought in bulk from countries with weaker economies, thus the price of the game is lower and so sites like these buy the CD Keys on the cheap on sell them to poor suckers who think they're getting a bargain only to have their key disabled. When you buy from CDKeyWorld and such sites you are not buying the full game, you are not paying the necessary price to own that game, because you are not paying the market price for the key and the publishers won't see a penny of the money you spend. It's tantamount to buying a burnt copy of a game from your friend.

If you want the game cheap, search around for truster retailers (supermarkets, established game shops) selling sealed, retail versions in a sale. Or simply buy from Steam direct.

But don't give these shady companies money from a CD Key they know you won't be able to use for long. Steam will ban it and they will be right to do so. Don't blame Steam, blame these scammers who are selling you a useless string of characters claiming to be a valid license to own a particular video game in your country.

Please take my advice, don't buy CD Keys. Either buy from Steam (or other trusted online retailers, D2D) or buy the game brand new and sealed. Read through this thread and just see how difficult they've proven to be, how people have had trouble receiving their products or money back and when you consider how shady they appear to be and add to the fact the product they are selling isn't authorised and thus the likely hood of your key being disabled it extremely high, then  it's pretty obvious that this company should not be dealt with. Employ some common sense. Pay the bit extra for a legit version of the game, if you use sites liked CDKeyWorld you'll lose your money. FACT.