saying sim not detected

It's fine before 8months and one fine I put my BlackBerry z10 in pocket and travelling to work place and in between the phone is saying technical problem and losing signal and I thought some error and restarted the phone and I got signal and lost again in 5 minutes and I surprising that all the pins in the sim tray are perfect and by seeing some tips I rubbed the sim glod part and put back I got signal for 30min and lost it said first technical problem and second time sim not detected and I am getting a message as device is network locked and contact service administrator. I want to know what is the problem it is with sim slot or phone......or software