I am very surprised that they did not do the PCW 'Health Check' procedure first, before replacing parts.
You may well find that part of the terms and conditions, it would possibly state that customer is responsible for back-ups, and PCW will hold no responsibility for lost data. I only hope that you did not have any sensitive material on the original hard-drive, because it as been known that sometimes, 'wiping' or total erasure of data is not completed according to company procedures.
If you want to take this further, then you could try Helen Grantham (Company Secretary) DSG Retail Ltd, Maylands Avenue, Hemel Hempstead, Herts, HP2 7TG. email@example.com