Let's review the announcements made on both twitter, discord, and forums.
Twitter;
We've got a brand new CHRISTMAS GAME plus treat yourself this Christmas 30% OFF STOREWIDE AND A FREE* T-SHIRT with every purchase made during December
*postage and packaging payable one per person. For full T&C's visit store.cubecraft.net" now from this it does give the hint it is free but it DOES state you need to pay for postage AND packaging
Discord;
INFO ON T-SHIRTS : After purchasing ANYTHING on store.cubecraft.net you will receive an email containing a unique code to you. Do not share this code, it will only work once and you only get one per IGN. You then go to merch.cubecraft.net and add any T-shirt to your basket. During checkout, use the unique code in the COUPON code box, and it will reduce the price of the shirt to ZERO! You will need to pay for postage and packaging to your country, but we ship worldwide. Please allow upto 3 hours for the email to arrive and check your spam folder before contacting sales support.
From this you can see it clearly states and I quote: "You will need to pay for postage and packaging to your country, but we ship worldwide." Therefore telling you once again you need to pay for postage and packaging
Forums post;
Firstly we've got a 30% OFF Christmas Sale with FREE* T-Shirts!
Today we're really excited to announce our Christmas Sale with 30% off all digital items! But that's not all - We want to make sure that you all have a GREAT Christmas - Thereforevery purchase made on store.cubecraft.net will receive a FREE* T-shirt!
But even with this if you continue to read on;
*T&C's Apply - You will have to pay for postage & packaging to your country, and the offer is limited to one code/free t-shirt per username. Offer ends 7th January 2018 or if stocks run out, whichever is sooner. The promotion can be stopped at any point without prior warning.
So in conclusion it says the shirt is free HOWEVER you will need to pay for postage and packaging is what the 5-10 is from.
