Anyone know of a phone scam that uses your cell phone to send texts to others? [View all]

I've been getting texts from someone claiming that I'm sending them nasty messages (apparently sexually explicit).

They sent the source phone number but that is not my number. I told the person this.

Despite this these texts continue.

I'm trying to decide if this is some fishing scam or some genuine hack.

I cannot see how that number comes to my phone (by text).

Anyone heard of such a thing?