Synchrony Financial Credit Card Complaint

Synchrony Financial Credit card department,

Late fee Pennsylvania

my daughter had - on -/-/2016. i put the $1500.00 on carecredit with synchrony bank. the terms were no interest if paid within six months. i set up my bank account bill payer to pay $250.00 on the first of each month starting -/-/2016. i have just received a bill for 5 late payments and interest on the entire amount for $300.00. they said i paid outside of the billing cycle and that every payment was late, not early, my billing cycle is the - through the - of each month. so because i was paying on the first, every payment was late, according to them, in my eyes it looks early but they said they can not accept early payments. so they said my initial payment was to just reduce my balance ( is n't that what all payments are for? ), and my second payment should have been paid between the - and the -. i think this is a very unfair practice. i paid the entire amount within the six month promo period and am still being charged $300.00, is there anything that can be done??