Why has my Tab S started to crash every time I use it after the software upgrade

[AC Question]

My Tab S 10.5 WiFi was automatically upgraded to Marshmallow last Thursday. That was the last time it was usable. It now crashes and switches off every time I try and use it, even when using it in "Safe" mode. I cannot be the only one this has happened to, but Samsung are taking no responsibility for it. The tablet is still under warranty, so I now have to go round like an ***** to try and get someone to sort it out. It's just not good enough. Anyone else having the same problem?