Have i been sold a dud????

[Northcountryboy]

Hi,wondering if anyone can help,Ive paid apple for the info but nothing back yet,ive bought an iphone 5s (first iPhone) that was meant to be on 02,the Tesco logo is showing but am not recieving a single dot on the call signal bar but when i put an EE sim in it gives me a strong signal but says sim isnt valid.I get a no service notice if i put it on 4G (i do have a 4G sim) but the Tesco logo comes up when i switch to 3G just no phone reception.I have tried all the things ive found on google but nothing works,Everything works fine on mates iphone with both 4G & signal so wondering if ive been sols a dud or its something i havn't yet done in settings.Running 8.4.Thanks in advance if anyone can help.