Countless times I have received that same message and received the same code that was used a long time ago. If I were to receive a message that I have earned $50 credit for being a loyal PSN member, the message would have to be from actual PSN officials instead of the scam spam message that people on your friends list have sent you.
Playstation Telephone Hours: Monday-Friday 8:00am-8:00pm PST (Closed on Saturdays & Sundays)
Customer Service - 1-800-345-7669
Account and Billing Support - 1-877-971-7669
Sony Rewards - 1-888-715-7669
Read the other posts, its SPAM
Customer Service Available Mon-Fri 8am - 8pm
General Enquires - 1-800-345-SONY (7669)
Account & Billing Support -1-877-971-SONY (7669)
Live Chat Available Mon-Sat 6am-10pm PST & Sun 6am-8pm - LiveChat
Don't bother with these types of messages. It's all phooey. Right now, there's a promotion PlayStation is doing that gives you $10 back for every $50 you spend on PSN through April 1st. If you did spend $50 before that date, you will get a message on PSN that will say, From [PSN] with a PSN logo beside it & subject saying, "$10 Credit" with an attachment on it. That is a legit message from PSN.
Homie From November 26, 2008 - September 13, 2013.
Shady business practices? File a complaint to the BBB.