I just got to know that someone received a text from me that I didn't send, what am I supposed to do now?

There are two possible scenarios for someone receiving a text from me that I didn't send : There is a virus on the sender's phone, or the SMS was spoofed, as per the SMS Spoofing link in your post. I think the most likely scenario is that there is a virus on your phone that WebRoot is not able to detect. A good way to check is to ask some of your other contacts to see if they have received a similar text. If this were a virus, I would expect your other contacts to have received similar messages. If this was done via SMS spoofing, this implies that whoever was trying to compromise the receiver's phone knew that the two of you had a pre-existing relationship, assuming they weren't just spoofing random numbers. This would imply a targeted attack.