I went through something similar a while back with a smaller platform, so I know how frustrating it is. The first thing you need to do is document everything: screenshots of your account, confirmation emails, transaction records, anything that proves you had that money there. Then, find out if the company left any official statement or if there's a liquidation process underway. Sometimes exchanges that close have to go through a legal process where users can file claims.
Contact the Consumer Ombudsman or file a complaint with the relevant regulatory authority (in Argentina it could be the CNV or the Central Bank, depending on how the platform was registered). It's also worth looking for groups on social media with other affected users, because sometimes they join forces to make collective claims. The truth is that recovering the money isn't guaranteed, especially if the company disappeared without a trace, but you at least have to try through legal channels.
If the exchange had no regulation or official license, unfortunately your situation is complicated. That's exactly what happens with many unregulated platforms: when they close, users lose almost everything because there's no protection fund. For the future, always go with registered and authorized exchanges, even if it's less convenient.