State Bank Of India [SBI] — unnecessary deduction of rs 4550

I have loan on my account but for past months I've been paying the emi's from different account of mine. On 20th sep my account was credited with my scholarship of 4550. The bank debited the amount mentioning ECS/ACS RETURN EXH. I want to know by what bills and by what calculations they took all the amount of 4550. I want my money back or i need a proper explanation with bills. U have no right to deduct this much amount exactly on the same date when the amount was credited.