Product: Credit card or prepaid card

I have a XXXX XXXX Citibank credit card. The HD card will automatically send certain purchases over a certain amount into their " deferred interest category '' for a certain period of months. XXXX or 24 months deferred interest depending on the amount of the purchase. The XXXX Citibank website is built to be super confusing. I understand the website, but am still getting screwed by this credit card. So, in order to pay off " promotional balances '' you must satisfy your minimum payment first, then any amount you pay in excess of that will be applied to your promotional balance. The kicker is, you must go into the website and navigate through a confusing maze in order to " allocate '' or pick which promotional balance you want your excess payment to satisfy. You can click up to XXXX promotional balances at a time. Your payment will be split XXXX ways. Here is my BIG issue, I had a promotional balance that was about to expire, the remaining balance was around {$920.00}, I clicked on this amount so that 100 % of anything extra I paid to my account after satisfying the minimum payment would be paid directly to this promotional balance so that I do NOT incur the HUGE penalty deferred interest of almost {$700.00}. Basically almost 85 % interest, even though they say its 29 %. That is a problem within itself, but that is NOT why I am reaching out. I am reaching out because I paid a single payment of {$920.00} to cover that remaining balance of {$920.00}. After making the payment and after the fee cleared my bank and cleared Home Depot Citibank card, I double checked to see if that balance had been removed...... Well... it had NOT. the HD card has taken my money, but NOT allocated any of it to the balance. I got on the phone XXXX separate time for at least an hour each time and was told that they had fixed the issue as they could see that my payment in addition to the minimum should have covered that {$920.00} promotional balance. They assured me it would be reflected in XXXX hours. So I would check back and it would NOT be changed, so that is when the multiple calls happened and each time they said they fixed it and NOT to worry, that when the new bill statement came out, I would get the accurate update. I just opened my new billing statement and was charged an additional {$670.00} in interest for the promotional balance that HD had agreed had been satisfied ... Fortunately, I keep up with this stuff or it would have just gone under the radar and been added to my total credit card balance. I called in today and they assured me that they refunded that full amount and I should see that reflected ASAP. They also are having to re-allocate funds for other payments I made that are NOT paying off promotional balances as they should. They agreed, I did everything right, but the system is not putting funds in the right place. My concern is how many past months have I been charged extra interest for promotional balances that I paid off, but were NOT reflected in the HD system. Also, once a promotional balance expires, a consumer/customer and NOT go back and see if our payments ultimately went to that balance, we just have to hope it did and watch to see if our interest that month went above normal. Here is where you come in, you guys need to do serious research on these promotional balances with Citibank Home Depot card and see if they are not allocating payments correctly and charging the consumer extra interest each month. This could be a HUGE scandal. If what is happening to me is happening to hundreds of thousand of other people, we are talking a major illegal scam to customers... I appreciate your help on this, I also have proof of all of my issues if you need to talk to me.