Dx Delivered Exactly

I have just been granted leave to remain in the UK and the government send your residency permit via DX delivery. I had scheduled a delivery for today between 1 – 5 pm, a service which I paid extra money for, in order to not have to lose an entire day’s pay waiting for them. Not only did they not show up, but their online tracking system says they did try to deliver and I wasn’t here. I had a missed call from a number I don’t know at 11 this morning, which was probably them, but they left no message, there was no card left saying they’d been here, and most importantly, 11 am is not between the hours of 1 – 5 pm. I now still don’t have my residency card, am out half a days wages and the fee a paid them for a service they didn’t actually provide, and will lose another entire days wages waiting on them to re deliver it again (because of the document they are delivering I can’t change the delivery address OR pick it up myself at the depot). Completely unacceptable service. Does anyone know how I might complain about them to the immigration office?