we are students. we are from bangladesh.

i live in guangzhou and my two friends live in wuhan and one friend lives in chendu. we all friends want to travel to south korea for 10 or 15 days. can we travel to south korea without visa for 15 days or less than 15 days?. please inform me. I called to the south korea embassy of guangzhou told me that need some documents to apply for visa and must need last 6 months bank statement. and then called to the south korea embassy of wuhan told me need some documents and last 3 months bank statement. And also then called to the south korea embassy of chengdu told me don't need visa for south korea to travel for a few days and we can travel to south korea without visa. so sir, i am in very confused about this. please can you inform me details about this as soon as possible. so i will be greatful to you.