Complaint sub-issue: Credit card company isn't resolving a dispute about a purchase on your statement

I opened an account with upgrade on XX/XX/2022. I opened a checking account and a line of credit. When I signed up I was promised a {$400.00} cash bonus if I opened a checking account and made 3 purchases in that account in the first 60 days. This is the whole reason I picked this company. The limit on my line of credit was {$7500.00}. My intention was to use this card for everything and then pay it off every month so I could build my credit and get the 2.2 % cash back on everything. I put all of my bills, gas, food, everything on the card and used almost the full limit. I made 2 small payments {$190.00} and {$500.00}. When I went to make my next payment it was showing that I owed more than my limit and I had just payed it down {$700.00} so I knew something wasnt right. I got really confused so I added up every single purchase ever made on this card and it came out to {$7800.00}. This does not include interest. Interest is added when you go to make them payment. So the total that I ever spent was {$7800.00} and I had just paid off {$500.00} plus {$190.00} which would mean that not including interest that I would owe {$7100.00} and upgrade was saying that I now owed {$7700.00} plus interest. I could quickly see there was a mistake so I called upgrade to see if we could get it resolved. I called 4 times before finally getting through to someone who basically told me that I was wrong and everything looked fine on their end. I tried over and over to explain the problem with no luck. The guy finally told me that someone higher up than him would call me back by the end of the next business day. I waited for a full week and never heard back. I called again and talked to someone named XXXX. She kept telling me everything was right and when I explained to her the issue she said give me a moment to review it and Ill come back on the line. She comes back 5 or 10 minutes later and says You have actually exceeded over {$10000.00} on this card I immediately told her we had not and asked her where she got that number from she told me that that is what the statement shows ( I was looking at the statement and it did not show that at all ) we argued back and forth and then she said she needed to send this to someone higher up and that I would hear back by the end of the next business day from someone named XXXX. We waited and waited and never heard from XXXX but we finally got through to XXXX in the resolution department and he was good to sit and help us we were on the phone for nearly 4 hours. At first he said the same thing Everything looks fine on our end but once I persisted he said Lets add everything up and go from there we added everything up on the phone and the total that we came to together was {$7900.00} at the end he said Oh yeah, youre right, I can see that something is wrong now, give me a while investigate, please stay on the line he came back after about a half of an hour and said when we apply payments to an account we have to do that manually and it looks like someone accidentally added your payments to your balance instead of subtracting them from your balance. Give me a while to fix this and then Ill be back I was so relieved and after a long time on hold he came back on and said So after further investigation it looks like I misspoke and everything on your account is as it should be we went back and fourth for a long time again and he basically just said Im sorry but Ive done everything that I can do. I can go back through the whole account again if youd like and then reach back out at a later date? I asked him to please do that and get back to me. He never did. I tried multiple more times to get through to someone and no one would help us. Every day the interest was racking up and it was making me so sick every time I thought about it so I ended up paying the full amount off and trying to keep reaching out. I have tried countless times to resolve the issue and I truly feel like the company is unwilling to resolve the issue. I was also promised that they would look in to my welcome bonus and why I never received it and i never got an answer on that either. The amount the I had to pay that I didnt owe was {$610.00} not including the interest that I payed on top of that. Between interest that I wouldnt have had to pay if the responded in a timely manner and fixed the issue so that I could pay off what I owed and the incorrect balance and the welcome bonus that I never got the company owes me close to {$1100.00}. Im very upset that they were unwilling to resolve these issues.