What made you keep all your coins in the same wallet is the first question that strikes my mind badly.

I believe this address was also involved in some HYIP investment activities like BitRegal (and maybe the admin was the guy himself who stole OP's funds)

Whole story below, please search for this address on that page: 12HfRnx47gQnnYn9Q3Zpiuzzv6yzXTKMEJ
https://x-invest.net/forum/thread-bitregal-10-daily-btc-only-13254?pid=184427&mode=linear

I've checked walletexplorer too and it's very strange that it is just a single address and no more addresses are in that wallet which made me believe it couldn't be of an exchange (maybe).