Worth you reading this thread:
https://www.volvoforums.org.uk/showthread.php?t=332362
and also the thread referred to in that thread.
Ignore the comment about going for a 40 minute drive on the motorway every so often as unless by fluke you just happen to time that journey with when your dpf filter reaches 100% (which is unlikely) all you will be doing is wasting your time and fuel! That is just something they say so that they can use the excuse that it is your fault due to doing lots of short journeys. Arguably it is your fault for doing lots of short journeys, but they might as well tell you it is your fault because you are driving the car!