DPD UK review: Delivery service

I sold an item that I sent with dpd to the buyers chosen pick up point and it showed via the tracking information that it arrived there on the 4th december. However, for some unknown reason the next day it got sent back to me. Dpd customer line over yfd phone could not help and even the what’s app chat just kept saying according to the tracking number it’s ’on its way back to your chosen destination’ but I want to speak to a human to ask why they picked it up after only 24 hours as it said that it can be kept for 7 days! Now the buyer is annoyed as she has paid (was sold via vestiaire collective) so I can’t even send it back as I won’t get paid. Vestisre do not know, dpd just said we don’t know ….. The tracking number is 155000537068799g.. Don’t tell me to track it as I don’t need to ask where it is I want to know why it was sent back to me after one day! I even spoke with the pick up shop that it got sent to and even they don’t know. Absolutely disgraceful as now I don’t know what to do as I won’t get paid £350 as the buyer is waiting to pick it up but dpd took it away again after only one day