Just an update on my original complaint.
I did contact OTB with all my evidence by phone and by email, but they said that this did not prove anything and that it was not possible for their website to cause such an error. The charges to change back to the original holiday, which I thought I was booking, would have raised the price further.
I decided against taking the complaint further, as it was causing me lots of worry and stress.
Instead, I have made sure that I pass on my experience of booking through OTB to all my friends and family, and I won't ever book through them again.
In the end we had a good holiday, but the apartments were not upto the standard of the major tour ops. I could have got a better standard of holiday through a major tour op for a similar price. We live and learn eh?
I've booked this year's holiday through Thomas Cook!