The difficulty you will have is proving that it was a BA computer glitch and not your error. Although you are convinced that you didn't make a mistake, it may be hard to show this.

On the payment page, where you put in your credit card details, the top of the page has a final confirmation of the names of the passengers and the days, dates, times and flight numbers that you're about to pay for. If you have a screenprint of that page, showing exactly what you were paying for and thus proving that it was a BA computer glitch after you clicked the button to pay and make the booking, that would be good.

But if you didn't make a screenprint of that page, then it will be a seriously uphill struggle. Of all the many complaints about the ba.com booking engine that have been made here over the years, I don't think I recall a single instance of "I can prove I booked X date but BA wrongly made the booking for Y date".

I make many ba.com bookings too, and I know that I make mistakes when doing them - including mistakes that I've only seen long after I've made the booking. So it may not be impossible that you did something during the booking process that reset a date field without you noticing it - particularly if you were doing this in a rush when you were pressed for time (which I infer to be the case as you absolutely could not have spared the time to sort out the error within 24 hours of making the booking).