it is necessary to go through agreement signed by you with bank for use of credit card . generally in case of cash withdrawals on credit card bank charges you 3%per month ie 36%pa . on bill being raised you can pay the entire outstanding with interest . it appears you have done so . if you had not paid full bill on due date and continued to use card for other purchases bank would be justified in charging you interest in month of January too
you can request bank to point out specific clause in your agreement which authorities bank to levy interest on further purchases made after raising of bill when full payment has been made on due date . you can also lodge complaint with bank Om budsman if you are not satisfied with the response . another option is to move consumer forum for deficiency in service .
