their 'guaranteed next day delivery' is not guaranteed

I know it's the christmas season and all post will be held up, but I ordered a jumper and a dress at the same time from boohoo, and paid for next day delivery, because if the dress didn't go with the shoes I could return it qucker. On my receipt it says I paid £5.99 delivery. The next day came and I heard a thud come through my letter box so I ran down to collect my items - but there was only the jumper inside. I emailed customer services, and no response, and emailed them the next day. I've tried tracking my parcel and because the jumper has been received, I've noticed that apparently my dress has been received too. Of course, I'm still waiting on the delivery, just like most customers on here. I only used their website because I'm skint, but after all this hassle it might just be easier to pay an extra twenty quid for a dress. Would like to use them again, however not sure that I will after seeing these other reviews.