Kiwi.com is Falling Short

I made a booking through Kiwi.com under reservation number 708979073 and paid extra for both a seat upgrade and the option to change my flights if needed. Within 24 hours of booking, I realized I needed to change my return flight to a day earlier and used the change option as intended. However, after changing the return flight, I was forced to pay an additional $50 seat fee for the new flight, while Kiwi.com refuses to refund the original $50 seat fee I had already paid for the first flight. In addition, the new return flight was cheaper than the original one, so I should actually be receiving a credit rather than paying more. Despite this, I have not been offered any refund or price adjustment, and I feel I have been charged twice for the same service. I have tried to contact Kiwi.com by chat around 75 times and have never received a proper response. There is a phone number listed, but it does not allow me to speak with anyone until a week before the flight, which makes it impossible to resolve this issue in a timely manner. I request that Kiwi.com provide me with a phone number or a direct way to speak with a real person about my case and refund the duplicate $50 seat fee, as well as correctly credit the price difference for the cheaper second flight.