Courier Guy Not Delivering on Promises

I am shockingly disappointed with The Courier Guy. I'm used to fast, excellent service, but I recently ordered something from Durban, which was collected on Monday the 24th of August. The Waybill number is UA***. When checking on progress, I suddenly see that the delivery was 'cancelled', so I followed up with the sender and they confirmed that the van did indeed collect it and that after calling the depot, found out that they've now lost my package. (This reeks of theft)

I want to know exactly what's going on and where my parcel is, because fobbing me off "it's somewhere in the depot" is not good enough.