If you had ordered them as your usual size and they were not the size then you could send them back as faulty as they were not as advertised. The distance selling regs say you dont have to pay for return postage if the item is faulty only if you have changed you mind. Probably not much use to you now but maybe worth remembering for future reference.
I sent a parcel to uni via myhermes a couple of weeks ago, 2 day delivery took 9 days
hope yours gets there faster.