Thanks very much for your responses. This is really helpful and seems I would have had a chance to contest the charge.
Unfortunately, I have now paid the amount as I was concerned about getting too close to the deadline and forgetting to pay it and it costing more money.
I now know the instructions mention about how to attach images and that responses can take 7 to 10 days.
Whilst I had skim read the instructions, I hadn't looked at the details as this sort of thing isn't something I'm very good at. Also, I am using my phone for this which isn't the easiest to carry out this sort of thing.
I feel silly now and sorry if I've wasted people's time. I'll know better for any future issues, hopefully there won't be any!