Why is my GT-15503 samsung not detecting my sim card?

i don't know if the problem is the phone the sim card slot because what ever sim card I insert nothing is detected

That's what happened to me but I have a Samsung Galaxy Ace I found out my sim card was not in the right way (Weird right) I nor my family had turned it around because I always have my phone with me. So try turning your sim card around as in around like not the other side the other way (I hope you know what I mean if not Just comment on this and tell me and same for anyone else x ) Hope this helped! :) ;)