Booking.com complaint: Flight booked 2 times overcharged

I booked my flight with booking.com on 27 May 2023 on FlyOne from Chisinau KIV to London Luton. When I got truth end of booking the website was showing me that this flight is unavailable, it suppose to be £170. I try then to book it for 26 May and get a flexible ticket which cost me £225 for me and my 8 months baby. When I check my bank account so I bean charged £225 twais. The company booked me both flight’s for 27 and 26th of May and charged me £450. Whe I call to cancel one of the flight the Booking.com asked me to call FullyOne to cancel it. However after 100 times of calls, FlyOne says the thikets are unchangeable and not possible to cancel it. On the day of flying I try to do the check in on FlyOne website, bat could not do it. I get to the airport on 27 May to get a help from FlyOne time as I could not reach anyone on the phone and been charged over 100 lei for training to call them. However when arrived at the airport no one bean at the FlyOne desk to help me with the flight. I lost £450 and not get my fly. Can you please help me with this.