SBI VISA Card ([protected]) — extra money demand

SBI offered me loan on phone for Rs.30000 for one year installment and I accepted, I paid every installment and dues in cheques, since SBI do not take any cash payments, I droped my cheque in SBI drop box in thrusday's, but according to SBI there drop box gets cleared on wednesday and because of this my actual due dates got over and I paid fine for this, and after all these I asked SBI for Full and Final due, SBI told me to pay a sum of RS.6824 and I have paid it by cheque, but in Feb 2008 SBI told me that I still have to pay Rs.17000, and I asked SBI for My full statement but they did not replied against it, but they have blocked my card and sent me a legal notice.