Three friends and I went to a concert at the biggest venue in Mexico City. One of my friends is a woman (this is important for the story). So, the concert ended and we agreed on a meetup point outside the venue so we could get a cab and leave together.
There were about 100,000 people there, so we inevitably got separated before going to the meetup point. We waited for my friend for about 15 minutes, then we started to get worried, so we called her phone. However, due to the sheer amount of people present at the venue trying to make phone calls, the lines were congested and the calls wouldn't go through.
After another 10 minutes trying to reach her, I get an incoming phone call from her. She sounded extremely gloomy and sad. She said "Hey [my name], I'm alright, I'm already at my place, everything is ok." I immediately got freaked out because this was impossible (she lived two hours away and not even an hour had gone by). We were super freaked out and tried to flag some cops down, cause it being Mexico City, I thought she had been kidnapped.
Then, 30 seconds after the call she comes out of the crowd looking chill. I yell at her, asking what the hell was wrong with her, etc. She looked so surprised at this. She denied having made any phone calls (she tried, but couldn't get a signal). We didn't believe her so we look at her phone and there was no record of the call having been made. I took my phone to show her the call and there was no record of the call having being received either.
To this day I have no idea what happened, because the voice on the other end of the phone was hers, and she knew details about me and my name.