Chromadek plate not delivered and payed for by client

We ordered roof sheeting from them. Payed extra for them to deliver it to our house. They send an email that stated that they wont be able to deliver on the day previously specified, only the day after that. While having lunch on the day prevously spesified the truck arrived to deliver. My husband only had a small time for lunch and went to help receive the sheeting. He did sign for it and went in to eat the rest of his sandwich. After eating we counted the plates and saw that there was one short. He immediately phoned the driver and told him to come and help counting it. (it was about 10min after delivery) When the driver arrived he also saw one was short. Contacting the office they kept insisting that it was impossible, thus in my opinion claiming that we must have stolen it. They are refusing to send us a new plate, saying we can collect it (we dont own a truck to collect a 7m plate). They wont pay back the money for the plate either. We saved a year to be able to buy the sheeting, we dont just have the money to write it off.