Why is my phone o

[Android Central Question]

My question is, why is it when I text someone who's on my contacts. I get a message back from a different number stating that I texted them? It's a number that is not on my contacts. The one who texted me, said what I said to the person that's on my contact. Please tell me why? Is it possible someone tampered my phone? Also when someone calls me they can't hear me say hello.