locker

I heard that it was possible to get your mog locker expanded by 40 slots, however i've only been able to extend mine by 10 (traded 4 mythril Imperial coins) and i've waited more than 24 hours (real time) and everytime I go to talk to the NPC by the mog house in white gate, he tells me that they...

Okay, what is a mog locker first. And second, how do I get one?

How? need to know ; ;