Did I text sensitive information to a stranger?

I have an iPhone that is connected to sprint, I've had 3 different numbers, the one I have and the 2 I had before.
Today I asked my friend to text me very sensitive information. I waited awhile and never got the text. I saw that she still had my very first number from a year ago. Since they were both iPhones I could see that the message was read?! But it wasn't sent to me. Who read the message that was sent to my old phone number? So I looked up the number in OkCaller dot com and it came up as the owner being me. My name popped up. So we called it but it only rang twice and went straight to voice mail. It wasn't only that time, we called through out the day with 6 different phones and with every phone it always went to voice mail after ringing twice.

Is it a number still under our contract that just isn't activated? Did a stranger get my old number? Because the message went from "delivered" to "read".

Phone numbers get recycled and issued to new people, in the days before cell phones, a number may have gone 6 months before it was re-issued. Now days with cell phones and many people giving up their old home numbers, more and more numbers are getting re-issued sooner, often as little as 30 days, which is why you can often get calls for months, from people looking for someone else or bill collectors also looking for someone else.

So don't worry about who has your old number, just make sure your friends, family and other contacts have your current number(s).