Product: Credit card or prepaid card

Around the beginning of XX/XX/2019, one of the authorized users rented a rental car from XXXX XXXX  at XXXX XXXX. The rate of which they offered them was approximately XXXX dollars per day. During the course of the rental period my card had been charged several times and when it reached it's XXXX XXXX I paid it down to approximately XXXX as I try to stay conscious of my credit balances. When reviewing the charges I noticed that there were multiple charges pending for XXXX dollars, XXXX dollars, XXXX dollars pending and XXXX dollars being held up for the rental fee. A few days later I noticed that the limit of my credit card was maxed out and over the limit again. I called Penfed the credit provider and inquired and was told not to worry those were pending charges. Later that day or the next day the charges were removed. When the rental car was returned the fees were 3 times that signed agreement a explanation was offered to the effect that " we can change the rate any time we feel without explanation. The car was returned and my card was charged somewhere in the neighborhood of XXXX XXXX dollars to  XXXX dollars. I am not sure of the amount because Penfed has allowed the merchant to submit several different charges that have been reflected on the statements as well as removing some fees only to add them back later at 3 times the amount. That has been the main issue. I don't understand what the fees are for and how they are what they are and no one at Penfed or the rental company with provide a suitable answer. A day or so later I disputed the charges I was told by XXXX on XXXX approximately XXXX p.m. not to worry the charges would be credited back until an investigation was completed. The next day I checked to see had the credit taken effect and was told by a different representative named XXXX that credit will be issued as well but could take 10 business days and I only had a few days left. Then a few days later I called again to inquire as to why I am not getting courtesy credit. The credit that several representatives had told I would get as I am concerned the over the limit will reflect on my credit report and tarnish my credit. I was told no worries, we will send you a letter to send to the bureaus to offset any damage. I was told that I am not being charged for the disputed amount, no interest, pentalties etc while the investigation is on going. Again, I asked why is that not reflected on my statement. After speaking with 3 supervisors that last of which named XXXX told me that I would not be able to get a courtesy credit while the investigation was taking place and that if I wanted to pay my card off then I would have to pay the disputed amount as well and in the event that my dispute was successful I would be credited back. As I told him that I am confident of that because had provided them with proof that I was over charged and if necessary I would take all legal action lawfully allowable to remedy the situation. I inquired about fraudulent charges of which he tried to explain the reasons of why I could or couldn't say it was fraud because I had saw in my portal when disputing the charges that that was an option however, after completed the call with him I checked to see if that option was still available and lo and behold the option was not available anymore for me. I feel I am being  discriminated against and not being given the benefit of doubt that most people have when disputing a charge. Any advice or assistance that you can provide to help remedy this in getting the actual amount that I '' m being charged valid or not is greatly appreciated.