Myntra.com — faulty refund

A week ago i have purchased 1 roadster men blue slim fit mid-rise clean look jeans pants for my brother.. But the size was incorrect so i request for return and the next day the product got picked and i received a msg "return picked up successfully" i accidentally change the return amount to myntra credit, that same day i got another msg "your return request for roadster men blue slim fit mid-rise clean look jeans (Return no : [protected]) has been processed. Refund of rs. 429.00 has been initiated to myntra credit". But i cannot use that amt why?