OpenCart: We don't receive an (admin) e-mail notification when order is placed.

When someone places an order in our Open Cart webshop, the customer DOES receive the order confirmation. But we (admin) don't receive any e-mail notification. Also please note: - the order is processed successfully and can be found in the backend, so no problems there. - when a new user registers, then we DO receive an admin notification (so the mail setting must be correct). - I have already tried more than 20+ plugins, none of them worked - already 2 developers have tried to fix this, but they couldn't resolve the issue - We have already checked the server log files, also nothing can be found there Please help, but note: - We prefer developers that work on this in the next 12 hours and get it fixed within 24 hours today. - Please don't reply if you have none or little experience with OC. - Please note that I'm looking for custom code to fix this, maybe some workaround. But don't try with existing plugins, they don't work for this issue!! - Please don't tell me the the mail setting are not correct. They do work and are tested. - We can NOT reinstall opencart - This is the URL: [login to view URL] - Our OpenCart version is 1.5.6.1