I would be discussing this on their twitter page, on their facebook page, on your facebook page and all over their twitter feed. And telling them that you are discussing it all over every musician forum you can name. Name and shame all over the internet. Write a song about it and release it on YT and make sure we all log into it and like it. It does not have to go viral to millions, they only have to have their dirty laundry shown in public in a creative way.
The thought that Parcelforce is not keeping records of online conversations is at the very least.......... strange. There is a reason every company in the world tell us that every conversation is recorded for "training" purposes.
This whole thing totally sucks and PF need to be dragged through the mud until they at the very least refund you.