WoT
 

I can purchase all the upgrades I want but I just cant purchase a new tank. Why? I have enough experience points but still have no option.

apart from the Premium tanks which can be bought for gold....you can only purchase tanks that you have Researched.
Check the Store to purchase - and Depot to sell (remember to take off any consumables etc and experienced crew before selling)

also if you have run out of garage space...save your gold and just sell Loltractor/MS1 to free up a space.

if you have lots of xp research points just check the Tech Tree to see how much you would use to get the tank you want.
Choose your path carefully cos there are a few shortcuts but not many
Can be a bit of a grind though.
Bare in mind there is gonna be a SoftWipe in a couple of weeks- whereby they will re-set everyones tanks but u will get your XP saved etc