Whether your item was delivered by Royal Mail or a courier is also important. 

If Royal Mail left your parcel in the recycling box because you told them to, it’s not the seller or Royal Mail’s responsibility if it’s now lost. It’s your problem. If Royal Mail left the parcel in the recycling box but you didn’t tell them to, it’s the responsibility of the seller if it gets lost. In that case you should contact the seller to ask for a redelivery or a refund. Do that by phone, email or write a letter.

If your parcel was delivered by a courier acting as delivery agent for the seller, it’s your problem if you agreed that the parcel could be left in the recycling box, or indeed if the terms and conditions of the seller or courier allow an alternative safe place to be identified and used at the point of delivery. Check the terms & conditions you have signed up to and change them if required so this does not happen again.

If you have agreed delivery to an alternative safe place, then again, it’s not the seller’s responsibility if your parcel goes missing. This is why couriers nowadays take a picture, to show the item as being delivered.

You will therefore be on much firmer legal ground if you did not agree to the parcel being left in your recycling box. In that case there is no doubt it is the legal responsibility of the seller to resolve the situation.

When ordering online, always make clear the item is needed by a specific date

You say the dress was bought for a particular purpose. A further nugget of advice is when ordering online is to make clear if an item must be delivered by a particular deadline. That way, if it is not delivered by the date requested you can ask for a full refund.

Under the Consumer Rights Act 2015, you can ask for your dress to be sent again if it was not received by an agreed date you specified at the outset or within a reasonable time – usually within 30 days. If you did not set a specified delivery deadline when you first ordered, make sure you do it this time. In legal speak this is called making “time of the essence” for delivery of the goods under the contract. 

If you do not receive the parcel, you can cancel and ask for your money back if you don’t get the item either within 30 days of buying it or on the date you have said it must be delivered by.

I hope you eventually get your parcel and enjoy your friend’s party, but please also note under the consumer contracts regulations, you have a legal right to a cooling off period. This means when you buy goods online you have additional rights to return them. You have the right to cancel at any time from when you place the order online and up to 14 days from the day the goods are delivered to you.  

Shopping online is all about the user experience being slick and easy to use but do not let that seduce you into forgetting your basic legal rights and be aware how retailers may try to manipulate the situation to their advantage. I must say your experience makes me want to stick to the high street, whether it’s exciting or not!  

Ask a Lawyer is written by Gary Rycroft, solicitor at Joseph A Jones & Co, and published twice a month on Mondays. Email your questions to askalawyer@telegraph.co.uk