after only 4 week of use of my new Nexus7 i head to reenter the PIN for my SIM more and more often.

Yesterday the Nexus always told me, that it couldn't recognize a SIM card.

I thought about contact problems and opened the slot to clean the contact fielf of the micro SIM card.

I was very surprised to find my SIM card damaged.

Beneath a lot of of heavy scratches i found a deap circular pit in the SIM card.
All this damages must be happened while inside the Nexus7, because i never removed the card.

Did anyone perceive simular symptoms?

Is there a feather or anything else inside the SIM slot, that causes pressure to the card, so it may be damaged?

Is there anyone who could tell me, how to solve this problem?
Each replacing of the SIM card costs me 16 EURO.