SIM card does not work in new iPhone

Hi

So i recently swapped over my sim card from an iPhone 6s to a 6 and i never seem to be able to connect to a mobile network. It always says searching or no service. I know for sure that this sim card works and have restarted, deleted network settings and even restored the phone but this problem still persists. There is no mobile data update and iOS is up to date. So what could i do to use mobile data with this sim card on this phone ???

Thanks for your time in advance