Whistl, which handles 26% of the UK's mail, .
As of today the company has stopped its E2E service - which was competing with Royal Mail to deliver packages and letters to people's doors. Tesco, Barclays and Lloyds all used the service.
Royal Mail has stepped in to help, but what happens and what are your rights if a letter or parcel doesn't show up? The good news is that the law's on your side.
“If a retailer fails to deliver your goods on time, they are in breach of their contract,” said John Pal, retail expert from the Manchester Business School.
“If you have paid for premium delivery and your order does not arrive before or on the date they said it would, you can apply for the refund from the retailer.
“A lot of people assume the refund lies with the delivery firm but actually it’s with the retailer.
"When you place your order with someone like Argos or Amazon, you agree to their terms and conditions - not the delivery company’s.”
We asked James Walker, founder of , what you should do if your parcel hasn't turned up.
"If you're expecting mail to be delivered by a company that goes bust, then you should still contact the person or company responsible for sending the document or package out in the first case, as it is them who has a responsibility to provide you with your goods," Walker said.
"In the case of Whistl, if you suspect a package is due to appear and it doesn't turn up, it's possibly also worth getting in touch with the parent company PostNL, although we're told that all outstanding Whistl Mail will be delivered by Royal Mail to peoples' homes and businesses."
Here are his top tips for people waiting for a delivery:
And if the shops still aren't playing ball, you can use this free service to find out .