Synchrony Financial Credit Card Complaint

Synchrony Financial Credit card department,

Billing statement Florida

I have a PayPal MasterCard account. I have been paying off a large balance the last couple of years due to a move. I was making extra payments and they were not being applied to the next months statement. They would still send me a bill. I called them once about it and said they ca n't do that and they need to return my extra payments. They sent me a check for around $2300.00. They never reversed interest on the years I have been doing that. They just refunded my last few extra payments. It just happen again. I sent a $500.00 payment for -/-/- and and extra $2500.00 that one would think would be applied for -/-/-. I just spoke to them and they said thats how they do it. I would like to know why they are allowed to do this and where is the protection for the consumer from these predators.