The dial on the watch from the replica forum is different then yours. Maybe look up photos of legit Monacos and compare them to yours?
Return it ASAP! If you paid by PayPal or credit card dispute the purchase right away.
Call Chrono24 and ask for assistance if you bought the watch on C24. Don’t wait any longer. Since their platform was used in a counterfeit watch sale, I believe they will make everything possible to help you to recover.
...or at least they really should, IMHO.