Kicker is talking about a total package from 100m Euros, while the sources in England are writing about a even smaller fee than Kepa, even with add-ons.
Sounds like the reporters from each country got their sources from their club in the country, so it will look like a good deal for both sides. In Germany they are trusting their sources and the same in England with their sources.
Chelsea themselves named him their "record signing" on their website. I'd be pissed if Havertz went for such a small fee after all but I' convinced the probability that the kicker report is wrong is very, very low.