Have you ever had things go bad in a house after a service change?

We upgraded a 200 amp service to 400, keeping one existing 200 amp panel and adding another. Everything seemed to go fine, but this morning one of my guys went to do some more work at the house and the customer said they had a burning smell in the bathroom and their cable modem was bad now. First they should've called as soon as they smelled the burning, but thats beside the point.
As it turned out, the GFI in the bath melted down, the cable modem or its power supply was fried and a surge strip melted down. That's all we know of at this time. I'll try to post pics of these devices later. What could've caused this? I'm thinking the POCO didn't turn the house disconnect off or the pole and the either hit line to ground or line to line. Unfortunatey none of our guys was there when the POCO did the switch over to the new mast.

One side note. The house was being served by #2 AL triplex overhead, from the house's original 100 or 125 amp service. We now have a 400 amp service and guess what? It's still being serviced by the original #2 AL. I'm going to talk to the engineer for the POCO about this, because he told me they would upgrade their cable, but they didn't.