Product: Credit card or prepaid card

Before I begin I want to communicate that I was advised by the company that if I file a complaint here it will go to the same department in their company and I will get the same answers. 
The situation is complicated. It concerns how payments are applied to the balances. The web site has no information or link on the Card Agreement so we can see them on the web page. I am referring to the Shop your Way page which is the main page concerning this account. There is also no link to the Citibank web site that has that information. This makes reading the card agreement very hard if we cant find it online. 
I had two balances on my account. Purchases 0 % APR until XX/XX/2023 and balance transfer ending on XX/XX/2023. 
Not being able to find the card agreement on the web page and with the solicitations being limited on information, I called customer service starting in XXXX. From the solicitations it appeared that the way payments are applied are as follow : The minimum payment would be applied to the balances that benefit the bank the most and excess payments would be applied by what benefits the consumer the most. 
Based on that premise I started calling the beginning of XXXX intending to pay off the Balance ending on XX/XX/2023 by that date when I had trouble with a few payments being correctly applied. I talked to multiple agents and no one really understands how payments are applied. I was told at various times different answers such as whatever the computer decidesno one really knows, balance transfers are paid first, balance with the larger amount is paid first and a manager told me that any payment made 30 days before the expiration of an offer will be applied to that offer. XXXX from the main office confirmed that all this was true. I purposely made a payment in the exact amount within 30 days of the expiration based on what the manager promised me but it was applied instead to the other balance. I called several times, First I was told it would be corrected and to wait 48 hours. After 48 hours I called and the agent made a complaint to the main office. XXXX called me and said that I can request it to be transferred and she would ask for it to be transferred and it should take less than a week. After a week I called and had to talk to multiple people until XXXX called me back on XX/XX/XXXX and told me that I was stuck. Why did it take her several weeks to find this out? Why did she wait until the end of the expiration period? She followed up with a letter on XX/XX/XXXX. Coincidentally it was right at the end of the offer and the extremely high interest would start to accrue. Could this be a scam the company does? 
Her letter stated, To be in compliance with governing regulations your payments in excess of the Minimum Payment Due are to be applied to the balances with a higher Annual Percentage Rate ( APR ) first. She then gave a list of how it applies. I am not sure why it took several months to be able to get this list. Nor is this list being followed. On XX/XX/XXXX, the balance changed to about 30 % APR. The balance transfer is still 0 %. I made a payment on XX/XX/XXXX for {$1600.00}. Most of this was excess payment. Instead of being applied to the balance with the higher APR, it was applied to the rest of my balance transfer. 
Neither the card agreement nor the solicitation for either program explains in any detail how payments are processed. I asked for them to review the solicitations I had received concerning both programs and was told by XXXX at the main office that the solicitations are no longer available as they dont keep record or copies of them. I find that extremely hard to believe. I sent one email back to them to show that it does not say that but it was ignored. 
Because I was not given written information in either the solicitations or the cardholder agreement on how the excess payments would be applied and since I was promised by numerous people including a credit manager and XXXX at the main office originally told me that it would be applied to the XXXX XXXX expiration date I did not have the funds available and am currently scrambling to get the extremely high APR balance paid. With so many agents telling me that it would not be an issue and it would be corrected they should follow through on what they said. How can they expect me to know if none of their people know?