If it was me I'd pay the extra and go at a time when everything I wanted to be there was indeed there. I had something vaguely similar this summer though it was my own fault - I'd booked the week before the summer eason starts and the park would have shut at 8pm - for us, in the summer, we adore the aextra 3 hours opening and it ended up costing £220 extra for the 2 of us to go the following week. Was it worth it? Yes, without a doubt - I had in my mind what In wanted on the holiday and it included the part closing late - anything else would have been a let down for us.
I would however keep on at the reservations department - write, email, phone. They should tell you that at the time of booking rather than giving you the impression you were booking exactly what you wanted without any doubt over parade dates. The small print may not cover phone reservations as you are not signing any forms to say you agree to all T&C - any uncertainties should be brought to your attention on the phone when you booked, especially when you highlighted the Fantillusion parade being such a big issue. I'd seek legal advice if they don't budge - you know you have been unfairly treated and you deserve to be fairly compensated.
I hope it all turns out ok the end for you.