HDFC Bank — Not received credit card fee

Have been offered life time free hdfc credit card with number 485498xxxxxx7934 with conditions that i have to make 4 transactions of minimum 500/- each every month for three consecutive months.
I did all the required transaction but still bank charged me 2500/- annual fee and 450/- igst towards annual fee.
I requested the bank for reversal of these charges and received a mail from bank stating that reversal of charges has been approved and will be credited to card account shortly, but still nothing has been credited even after 20 days of email.
Reference number [protected] was provided by bank in this regard.

Please look into the matter and try to solve the issue at earliest