U.S. Bancorp Credit Card Complaint

U.S. Bancorp Credit card department,

APR or interest rate California

US Bank credit card with zero percent offer balance & purchases. Although the purchases are being paid off monthly, the bank still charges an interest charge because there is another balance on the card ( at zero interest ). contacted the bank every month it occurs however the reps just reverse the fee and tell me to call again when that occurs instead of working on fixing the issue. Payments must go to higher interest balances first so paying off the purchases before the due date should not cause any interest charges.