i bought my apartment in Jum Village sth from Minc Properties (via dubaiwaterfronts) and they sent the receipts on time. I think they also have a london office. Have you contacted Minc about the overpayment, and was the rental guarantee suppose to start from completion or a particular date...what does the contract say?

I think nearly all new developments being released now in dubai and even places like ajman are getting sold out. So people are still buying, it's just that not much is being completed on time (well nothing is for that matter). Remember, you can always sell and run with your money if you feel the heat!