This promotion runs from October 13, 2017 until January 8, 2018. From what I can find, this action is exclusively available in European countries. Details about the UK action can be found over here.
The following Samsung SSDs are covered by this action, but bear in mind you need to buy them from a participating retailer:
850 EVO 250GB MZ-75E250B/EU 850 EVO 250GB MZ-75E250R/W 850 EVO 500GB MZ-75E500B/EU 850 EVO 500GB MZ-75E500RW 850 EVO 1TB MZ-75E1T0B/EU 850 EVO 2TB MZ-75E2T0B/EU 850 EVO 4TB MZ-75E4T0B/EU 960 PRO 512GB MZ-V6P512BW 960 PRO 1TB MZ-V6P1T0BW 960 PRO 2TB MZ-V6P2T0BW 960 EVO 250GB MZ-V6E250BW 960 EVO 500GB MZ-V6E500BW 960 EVO 1TB MZ-V6E1T0BW T5 250GB MU-PA250B/EU T5 500GB MU-PA500B/EU T5 1TB MU-PA1T0B/EU T5 2TB MU-PA2T0B/EU