Be sure to file a complaint against EGI through the BBB for not officially employing a method that attempts to retrieve hard-earned player data in the case of an accident, such as the inevitable console freeze that has the potential to affect all players.
What has happened to you is a common problem that is known to both Epic and Microsoft. Neither entity will do anything to help get your rank back, so don't bother wasting your time contacting them. Unfortunately, the bottom line is that aside from backing
up your player data file (to the cloud or external flash drive) there is no way to recover your data and some of the medals will be permanently locked. Your choices now are to start ranking up from scratch all over again or move on to another game. If you
choose the former, be sure to back up your data.
If you search the Gears 3 threads, you will find countless topics that deal with this issue.