Can I get the tax band of my car changed?

I have owned a 2014 Volkswagen Caravelle 2.0 TDI for the last 3 years and have pad £340, £360, and £395 car tax for those three years. It states on my registration document that the CO2 is 203g/km but...

Why is my 2013 BMW so much more expensive to tax than a 2018 model?

I have a 2013 BMW M6 and pay over £600 in VED but the 2018 model with same emission is £180? Seems a bit unreasonable.

Why did I not get an emissions sheet with my MoT certificate?

I’ve just bought a 2012 Vauxhall Zafira for my daughter with 60k miles. The dealer had a local MoT Station provide an MoT before we bought it but we were not given the emissions sheet. After just 10 days...