Product: Credit card or prepaid card

Synchrony Bank charges interest on purchases made previous to the statement date even if I pay the full balance due before the Statement Due Date. 
I use a Care Credit Rewards Card. If I make purchases on the Revolving Charge Portion of my account I get charged interest even if I pay off those charges before the STATEMENT DUE DATE of the statement on which those charges appear. I talked to XXXX  ( agent number XXXX ) on XX/XX/2020 just before noon. He stated that any purchases must be paid off by the STATEMENT CLOSING DATE in order to avoid paying interest. This STATEMENT CLOSING DATE occurs before I have even received the statement in the mail. The STATEMENT CLOSING DATE is generally about 3-4 weeks before the STATEMENT DUE DATE. The problem is that this method of charging interest is contrary to every other credit card that I use, or have used, or ever heard of in my entire lifetime. I feel that this is a scam purposely devised to deceive users into having to always pay interest. I called Synchrony Bank many times previous to XX/XX/2020, and expressed that my purpose was to always avoid paying interest. All of these times that I called Synchrony 's method of calculating interest was never explained to me. On XX/XX/2020, a customer service rep even removed the interest charge on my XX/XX/XXXX statement, apologizing for any inconvenience, but not really explaining that the method of calculating interest had caused my problem. I stated on that date, and in previous conversations with customer service, that my sole intent was to avoid paying any interest on the Revolving portion of my account, and that I try to pay off my Revolving Balance every month. As it is, I have to call Synchrony every month in order to separately allocate portions of my total payment to my revolving charge, because if I don't call, there is no possible way to apply the total payment to my revolving balance, as opposed to my promotional balance which does not incur interest every month. I feel that this is another deceptive practice by Synchrony, because Synchrony purposely will apply a payment to a Promotional balance, which does not incur interest charges until after 6 or more months, before it applies payments to a Revolving balance, which does incur daily interest charges. This is also contrary to the method that other credit cards, like XXXX XXXX, use to apply payments to revolving and promotional balances. 
On XX/XX/XXXX customer service rep XXXX refused to make adjustments in the interest charge on my XX/XX/XXXX statement, saying he was not allowed to do so, even though a previous customer service rep had done so on XX/XX/XXXX for the previous statement. He also tried to abruptly close our conversation saying that there were too many people in the queue behind me, and refused to pass me on to a manager or give me any other contact information in order to escalate my complaint. 
To sum up : Any purchases that I make on this card will ALWAYS incur interest, as it is pretty impossible to pay them off before the STATEMENT CLOSING DATE. I would have to pay each purchase on the card the day after I made the charge in order to avoid paying interest? This is not a " credit card '' in the normal sense of the term, nor does it seem an ethical way to do business.