Try a better fuel, such as Shell V-Power diesel or BP Ultimate diesel. Kia 1.6 CRDI are very reliable but not the most economical. If you have the ECU remapped you have to declare it to your insurer and the premium increase will more than wipe out any saving. You car is probably EU6, so faces penalties for entering London's ULEZ and ULEZs in other cities from October 2020. The only ways to avoid this are to get an EU4 or later petrol engined car or an EU6 or later diesel.