Barclays Credit Card Complaint

Barclays Credit card department,

New Jersey

I purchased a Laptop from - and at the time of purchase, - had or still have financial options and Barclay visa card was the option so, I applied for the credit card, got approved but Barclay had a not interest if paid by certain date and now Barclay is charging me all the interest accrued from day one but, the balance from that particular purchase was way down and I feel Barclay should only charge interest for the remaining balance.