If a retailor accidently sends me the wrong item in the mail can i legally keep

Hello, i ordered a 35$ womans shirt from a retailor and they sent me a 158$ mans jacket instead. i was upset that i got the wrong item and called them to let them know right away. the lady said she would send "my complaint" to corporate and theyd call me back. i got a e-mail saying "return the wrong item for a refund or exchange and heres a 15% off coupon" if i keep the jacket can they legally come after me for the $ difference???