UPDATE: There may still be some issues with this achievement unlocking. A support ticket has been raised with Valve. I'll post any updates here.
Original post follows...
The 'Paid in Full' achievement has now been fixed. This achievement was not unlocking when you hit the 50,000 point requirement.
The fix has been published in the Steamworks back-end, therefore no update is required to the game itself.
Apologies to the 2 people affected by this. The rest of you need to step up your game!