my phone was in repair, i cant activate my phone using my apple id.Pls help?

Plug it into your computer you did your last backup on. Right click on your restore iPhone and pick a date on it when it was working right and restore it at that time when your restore point was working right. That will restore it to the point when it was working right and it should fix the problem. I had to do mine like that when I changed carriers so I went back in my restore point when I had my original carrier and it reset my APN's back to my original carrier. It should rest your phone back at a time so your iTunes will recognize your phone again.

Who repaired it? If you took it to a 3rd party and now it's stating that you must use an Apple ID other than your own to activate it, that means they put a used, activation locked logic board in it. Take it back to them. You will not be able to activate it if that's the case.

Apple does not sell iPhone parts at all. The only sources are counterfeit parts, stolen parts, or salvaged parts. I'm guessing that your logic board was replaced with the latter.