SIM 512k not detected after having changed carrier

Hi!

I have a Google Nexus 5 bought used (in perfect conditions though) from Amazon about one year ago. I never had problems with it, until a week ago after having changed carrier and having received a new 512k NFC SIM card my phone keeps saying "no SIM card inserted". The SIM itself works perfectly (I tried iit on other mobile phones, though not my same model), and my phone works perfectly with SIM cards of older generation (I tried a friend of mine's two year old SIM card and it worked perfectly). I asked my carrier to substitute the card and they gave me another one of the same generation: the problem persisted. Any ideas?