My SE is asking for another persons Apple ID after I have re-set it.

I bought an Apple 5 SE (1st gen) new from a department store several years ago, I used it for a long time and only upgraded recently to the Apple 12 mini, purchased new again from a department store. I transferred all data to the 12 and kept the 5 in my possession just in case and as a spare. During my time with my SE, I had my macbook pro stolen in Barcelona and that was never to be seen again. I am now trying to use my SE now as a back-up phone but it is not recognising my passcode anymore. I have done a full factory re-set in the hope that this would help, it has asked me for my apple ID which I entered, it says incorrect. It says that it is locked to the owner but I am the owner and always have been. It says to unlock this phone, enter the apple ID and password that were used during setup. Someone M*****@icloud.com, this is not me. It asks if I want to use the activation lock help, it now says, a password is required to activate this device because its owner has used find my iphone to link it to their Apple ID. I thinks that I am not the original owner and I can only assume that someone used my stolen macbook to find my iPhone! Nothing I have tried will get me in to my phone, what now?