State Bank Of India [SBI] — Wrong balance shown

Address: Gondia, Maharashtra, 441601

MY SBI account was credited with Rs 24000. I withdrew Rs 4000. So the available balance should be 20000.But The Bank shows my balance to be 16000 and also a LIEN amount of Rs 8000.I have never applied for any loan nor do I have a credit card so question of dues doesn't arise.I don't have paid anyone in cheques so there is no chance of cheque bounces. still the bank shows this lien amount .they have deducted money with no reason. They haven't even mentioned this deduction in account statement.I'm utterly confused.how should I go about it?