Hello Cespian - thanks 4 the welcome !
The problem was not that it did not fit - it fits perfectly. The problem was that they sold me a sub-ohm tank+coil which is a specialized product for specific batteries.
If they had said "Do you have a sub-ohm capable battery?" I would completely...
So I went to VAfrica to get a new tank. I told them I don't need a battery as I have some old ones laying at home. I bought the tank they recommended not knowing that it was a sub-ohm tank that requires one of the newer batteries to operate.
Took it home - didn't work on any of my batteries...