Yes you can eat chicken after the use by date if it's frozen.
The use by date is a general guideline as to when you should eat the chicken before it loses it's freshness and best taste.
So it's best to eat the chicken before the use by date if you want fresher chicken and a better taste but as long as the chicken has remained frozen past the use by date and has remained frozen as long as you've had the chicken the chicken will be safe to eat.
You can keep chicken for a year and sometimes longer past the use by date as long as it's remained frozen.
The freezing temperatures keep the bacteria off the chicken so it remains safe to eat well past the use by date.
I've kept chicken for 2 years in the freezer before and then cooked it because I forgot about it at the bottom of my freezer and it was still safe to eat.