iPhone 5c (US version) wont accept Nano sim

Get a nano SIM from your carrier. If the phone is carrier locked, the phone will not "see" the SIM if you use a SIM from another carrier. You must get the carrier to which the phone is locked to unlock it for you.

Where did you buy the phone? Full price is not necessarily unlocked. And SIM free is NOT unlocked.

An iPhone that is sold "sim-free" is not an unlocked iPhone. It is only unlocked until a sim is inserted and it is activated. At that point it becomes locked to that carrier. You cannot change the carriers after you have activated a sim-free unit.

Why did you cut the SIM by yourself? Why did you not get a Nano SIM from the outset.? Cutting the SIMwas a foolish thing to do. Bits of the cut nano SIM probably screwed up the SIM slot. But I am speculating.

In any case, I would recommend you take the phone to an Apple store for evaluation, but you will be unable to do so as I believe you are in EU and the warranty is not international. You must tkae the phone to the US for service.

OK, so you purchased an officially unlocked iPhone, but it only works with a sim card YOU cut down, not a stock nano sim card, is that correct?

When you first inserted a sim card, was it one YOU cut down? If so, this "may" be the source of your issue. A stock nano sim card is slightly thinner than a micro or standard size sim card. Could be you "damaged" things by using a cut down sim card. Obviously I can't say for certain, but sure looks to be the case.

If you bought the iPhone in the US, and are not in the US you cannot take it to Apple for service...the warranty on iPhones is only valid in the country of purchase. Apple in Europe will not touch a US-purchased iPhone.

Selling might be an option, or if you know someone in the US you trust you could ship it to that person and have them take it to an Apple store genius bar for help. Apple will not accept shipments from outside the country of sale, but if you can get someone in-country to reprent you they will deal with it.

What you think is irrelevant. Anecdotal evidence indicates that you probably damaged the phone. Only Apple can tell. As stated Apple in the EU will not touch the phone. So your choice us to take the phone yourself to the US or send it to a friend so he dan take it. And as damage is not covered by the warranty you will have to buy an out warranty exchange.

"Lo barato sale caro."

Time to move on.

Just sell it the way it is, but state the situation so potential buyers can evaluate on their own. If the sim slot is damaged, the phone will have to be replaced to fix.