[Ben Hur]

vovlomum, If you are going to complain to those that you mentioned I recommend that you have as much information as possible and from your well written post I see the following is missing:

You bought the V70 from a dealer, is this a Volvo dealer or a used car dealer?
What was the millage on the V70 when you bought it?
How many miles did the V70 cover when you first had the problem with the DPF 4 weeks later?
How many miles does the V70 cover between each DPF problem?
What fuel are you using? (name of supermarket or brand and product name)

I ask the last because I think, sorry I can't prove it!, so that's why I say I think that if you use a fuel like Shell V-Power Diesel you would have less DPF problems. My thinking is based on the following emissions information:

Regular Diesel BS EN 950 maximum parameters
Carbon Residue 0.3% mass, Ash 0.01% mass, Particulate Matter 24mg/Kg

Shell V-Power Diesel maximum parameters
Carbon Residue <0.1% mass, Ash <0.001% mass, Particulate Matter 2mg/Kg

Based on these figures the Shell V-Power Diesel gives significantly less Particulate Matter and it may turn out that using cheap diesel could be partly to blame for this problem.