UPC mobile coverage issues?

Anyone using UPC? I am facing no mobile date coverage in various parts of Zurich city! For example, Zurich Oerlikon! Every time I visit Oerlikon, I don't have mobile data coverage! I can make phone calls and send SMS but no mobile data so can't use internet, WhatsApp etc.

Normally on top left corner of my Android phone I see provider as UPC CH but when I am in Oerlikon I see Swisscom| UPC CH . It is not case of a few meters but whole of Oerlikon My friend is with UPC too, and he has the same issue.

Any idea what is going on? I called UPC but they were useless. I will call again, but I thought I ask here first.

UPC use Sunriseā€˜s network, which is patchy. I left Sunrise 12 years ago because of poor coverage...

The thing is that until recently I was with Sunrise and I had no such problem in Zurich. Now Sunrise and UPC are one though