Anyone know of a phone scam that uses your cell phone to send texts to others?

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?