If $T_{1}\subset T_{2}$ and $T_{1}$ is complete and $T_{2}$ is satisfiable, then $T_{1}= T_{2}$

Question

If $T_{1}\subset T_{2}$ and $T_{1}$ is complete and $T_{2}$ is satisfiable and both are in the same language , then $T_{1}= T_{2}$

I know a set is complete if $\forall y, y\in T$ or $\neg y\in T$. But I don't know how to apply this towards an actual proof. Can anyone help?