The use by date on chicken and other meat is just a guideline as to when it should be eaten for freshness but even when the use by date has passed it doesn't mean that the chicken or meat has gone bad.
As long as you keep the chicken frozen you can eat the chicken for a year or more past the use by date.
If the chicken smells good and isn't really slimy then the chicken is perfectly safe to eat and you can go ahead and cook and eat it.
You don't always have to use the chicken before the use by date unless you want too.