ABN AMRO Credit Cards — Reversal o[censored]nwanted amt. charged

I am holding abn amro bank credit card (titanium) for last 3-4 years. Last year in Month of Oct. they have charged me 4500/- against some hanky panky previledge card offer. I would like to insist that they have debited this amt. without my approval for the offer. Recently also they have tried to trap in such type of offer. In very next month i.e. Jan.2009 i contacted the Customer care of ABN Amro for reversal of the amt. debited to my card. They asked me return the voucher (unfilled, because i got them in month of Jan-09) so i returned the voucher which they never acknowledged and never reverse the amt. till date....Till last month i use to pay this or that amt. to them on the hope that they will reverse the amt. Today only I received a call from collection department, the executive used harsh language and insisted for payment. He dare to talk me that i had accepted the offer so the amount can not be reveresed... they regularly use to call me on my home telephone number also for the payments. I have many times requested them that i would like to pay any dues with me but first they reverse the amount debited to me... i am using many other credit cards and have excellent track record with all of them.. i am a reputed business man and want to pay the dues to settle the matter. But ABN AMRO customer care is so worst that they just don't respond to my problem... My card No. is [protected]