Needs a code for stereo 5000 RDS EON?

I had to change the battery in my car, so I need the code for my stereo. Hope someone can help me :) Car: Ford Mondeo 96 Model Stereo: 5000 RDS EON. (No cd player, cassette player only) Serial No.: M21390 - I'm not quite sure which of these two is right, but here is the other serial number. : M213908. But I think the first serial number, which I wrote down is the correct serial number. I also tried to find the correct code a few times before, so now when I turn on the radio, it comes up "Locked" on the screen. So if anyone has any tips on how I can get rid of this, it would be great. I really hope someone can help me with this problem :)))