Why did they do the pre op assessment when there's no op date?!?! I can only speak from my experience but I've never had a pre-op more than 2 weeks before an operation.
You need to get on to your gp and get him/her to write to /call the hospital consultant. You also need to get in contact with the gynae team/ consultant yourself. This might mean calling them several times a week or putting something in writing. If you are REALLY annoyed, you can get in contact with the hospital's PALS team or the chief exec's office. It's ridiculous that they have left you hanging for so long!
By that same token, if you need to postpone, tell them sooner rather than later - they can give the spot to someone else. They ought to pause the 'clock' and give you a date in the not-too-distant future....but it might be a few months (I postponed once and had to wait 4 months for the next date but I didn't mind this).
What do you think you'll do? I hope you get things sorted in the very near future.