I've finally heard back from Hiribi support, and so far, they seem willing to help me out. I'm waiting for more information from them regarding the transaction that was flagged as unauthorized, before I then try to solve the limitation issue.

Months ago, exchanges above $1000 went through fine for me. Not this time, though. To anyone considering this service, I would exercise extreme caution, and don't try to exchange huge amounts, especially if you're not already transacting regularly big volume in your PayPal.