You have to redeem a code for your free PS Plus day
If you had an active PlayStation Plus subscription on January 4th, 2016, you're entitled to a free 1-day extension. But you need to redeem a code manually.
Those affected by the recent 1-day outage of the PlayStation Network are being compensated with a 1-day extension to their subscription. But you need to keep an eye on your mail and redeem the code that’s sent out.
PlayStation Plus subscribers are being sent voucher codes to redeem for the free day rather than having it applied automatically to their account. If entitled to an extension, you’ll find a mail in your inbox titled ‘PlayStation Plus membership extension’. Your code can be found in that e-mail.
All those with an active PlayStation Plus subscription on January 4th, 2016 are entitled to a free day. You need to redeem the code by March 31st.