Not a key buyer myself but I've heard that there's two kinds of limits: one for simply buying too much in a certain time frame, and another depending on your character's total level. So try increasing your total level or wait up is my suggestion, if you really want to waste your money on keys.
I thought there would be a limit too, but after some further investigation I found this:
"Keys can be bought in groups of 15, 35, 75, 200, or 450 keys, with a respective 40, 120, 400, 1,200, and 3,000 bonus Hearts of Ice given to the player upon purchase. There isn't a cap on how many bought keys and Hearts of Ice that a player can have at a time. Players can spend an unlimited amount of money on keys. Players can only buy 20,000 keys in a single day. There is no monthly maximum when purchasing keys."
There are key buying limits. (That is the old unsupported wikia that you gave the URL for. A link to the supported wiki is found Under "Game Guide" in the menu at the top of the page.)
Here's are J Mod responses from similar past threads:
Original message details are unavailable. I understand you've been having issues with your buying limit having been reached for Treasure Hunter Keys. Limits for purchases are based on a number of factors. I am unable to go into detail on what these factor are, as truthfully I don't know. What I do know is that previous purchases are taken into consideration but it is our systems that sets what quantities you are allowed to buy in.
I am also unaware of when this limit will be lifted as it depends on a number of factors that the system decides but hopefully it will not be too long. t this can be frustrating.
Original message details are unavailable. As I mentioned, the system sets these limits, unless you are buying through a third party such as BOKU, who set their own. This is not a widespread issue and only impacts very few players, as it usually takes quite a lot of purchases, to trigger the limit being imposed.
Please be aware that the limits are there for the best interests of all parties and I hope it hasn't impacted on your gaming too much, but the limits will not be lifted until the system makes that decision.