Product: Credit card or prepaid card

First off I would like to say I have been greatly affected by COVID 19. I lost my job on XX/XX/XXXX due to the business I work for closing down. 
I had a credit account with Comenity LLC at the time. On XX/XX/XXXX I received an email ( the same email I usually receive once per month that tells me how much is due, date due and the total balance still owed ) it showed a payment of {$35.00} is due on XX/XX/2020 and it showed my current balance was {$410.00}. Even though my payment due every month is only {$35.00} I ALWAYS make a minimum payment of {$100.00}. ( I have statements to support this ) XXXX XX/XX/XXXX i made my usual payment of {$100.00}. On XX/XX/XXXX I received another email that again, displayed my payment due, date due and balance, but this time it said payment due {$51.00}, date due XX/XX/2020, total balance due {$1200.00}. When i seen the balance i was very concerned because i didn't understand why my total balance due increased by nearly {$900.00}. I have NEVER missed a payment ( I have statements to prove this ) and i have NEVER paid only the minimum amount. I immediately called Comenity to get some clarification on the added charges. I attempted to call them on Monday XX/XX/XXXX but I was unsuccessful to getting through since it was a holiday. I waited until the next day, Tuesday XX/XX/XXXX. I called them at XXXX XXXX on XX/XX/XXXX. I explained my concerns for the additional {$900.00} on my account. The person I spoke to told me the added charges were from interest that had been accrued from the time I opened the account due to the " promotional period '' ending. I didn't understand nor did I ever receive and email stating " Total balance must be paid in order to not be charged interest. '' I told them I recieve the same email every month which shows payment amount due, date due, and total balance. I told them how this could have happened if I have NEVER missed a payment and also how this could have happened if I pay more than my minimum every month. I also expressed to them that I lost my job due to COVID 19 and that these charges couldn't come at a worse time. They were not sympathetic to me being affected by COVID even though on their website they have " provide support and assistance to those affected by covid. '' Instead they said they could open an investigation on my account to see if the charges were by accident and that a credit would be issued if the investigation shows it was a mistake. They told me i would receive a letter in the mail just confirming the ongoing investigation. When they asked me to confirm my address on file they had an old address which i lived at 2 years ago. That also confirms i haven't recieved any paper statements in the past 2 years. I waited for the investigation to be completed and I recieved a letter from them on Monday XX/XX/XXXX stating their investigation is completed. I didn't understand the rest of the letter so I called them again to get some clarification. They told me the investigation was completed and no changes will be made to my account. The lady was sympathetic and she said if I had been affected by COVID 19 and had difficulty making payments i was suppose to contact them by XX/XX/XXXX. I told her my original call was on XX/XX/XXXX so it was definitely before XX/XX/XXXX. I tried to explain to her that I would have been able to continue making payments when my balance due was {$410.00}. I told her my difficulty didn't occur until I had the " accrued interest charge '' of close to {$900.00} added to my total balance. I was not aware that my " promotional period '' was ending. I explained I recieved an email on XX/XX/XXXX showing my total balance due was {$410.00}, then all of a sudden ( 8 days later ) on XX/XX/XXXX i received another email showing my total balance due was {$1200.00}. I didnt get an email saying anything along the lines of " You must pay your total balance due or else you will pay close to {$900.00} in interest fees. Of course if i would have know that I wouldnt have hesitated to pay off the total {$410.00}. I told her I also didn't agree with the outcome and I feel as though maybe the additional interest could have been pushed back to a later date since I had been negatively affected by COVID19. Comenity has been very unfair and is very " one sided '' they are not sympathetic to those affected by COVID19. I would like assistance in resolving this issue since I feel they have not been of any assistance to those hurt by COVID 19.