Locker already full

For the second time in 6 months I have taken a parcel to drop off in an allocated PUDO locker, and the locker already has a parcel in it. How does that even happen if they can only be opened with an allocated PIN ? To make matters worse the response I recd from PUDO was " We will cancel the order and credit your account". No apology. No sorry for the inconvenience and the waste of your time and petrol ! Once is bad enough, but twice !! Very disappointed.