Turkish Airlines Extra Baggage Charge Issue

I purchased 54 kg of baggage through the app and paid £141. At the airport, they told me I only had 20 kg. I called customer service to explain the situation. I stated that everything was recorded and that £141 would not be charged for just 20 kg of baggage. They told me that the price was quoted for 54 kg and that it was a system error. They suggested that I pay the extra fee now and get a refund later. To avoid missing my flight, I paid an additional €105 at the airport. Ultimately, it is not acceptable for Turkish Airlines to take our money. I called customer service twice to request a refund, but received negative responses. I also applied once through the website and received another negative response. I know my conversations are recorded, and I will seek my rights through legal means.