The unlocking of the igloo floors it is NOT enough to have collected the keys! It can’t be achieved by a player by himself/herself.
All players of your region (Egypt, Scandinavia, China, Atlantis, Greece, New World, Terra) build your region-igloo together.
When all players from your region have accumulated 100% of the ice that is needed for the igloo, you are able to reach the topmost floor.
At this moment, none of the regions have opened the 8th floor.
All info in these threads:
(by @MadameCurie ) If you have questions, ask them in this thread:
Did you check in your INVENTORY > MISC?
Is there the key 6?