Bestbuy / Citibank N.A. Tricky / faulty billing practices Nationwide

Bestbuy's billing practices are tricky and very misleading. Over $1,000 in interest was added to My24month promotional purchase balance amount of 1,646.57 because I made additional purchases within that promotional period, and some payments applied to my balance went towards paying off the purchases I made after the $1,646.57 purchase. I called and spoke to customer service about the situation and was told that I could of called and stated how I wanted my payments applied. WHAT???  I am not into accounting and would just like to make purchases without being ripped off. Now my original purchase amount adds up to $3,000. Watch out for bestbuy / Citibank N.A. for their billing and financing practices.