Prepayment screenshots necessary

Booked & paid for a flat in Stellenbosch, using the Bookings.com app on my phone. Price was advertised as R2170, but R3100 was charged to my credit card & showed on my bookings confirmation. Contacted Bookings immediatly, but no help. I have to prove to THEM, what price was advertised on THEIR website at the time. So beware, always take screenshots before paying!!!