After reading all this written I came to the conclusion that no one has managed to solve the problem.
My problem is similar.
I am the owner of a Mazda 3 1.5 diesel for 2 and a half months, the car is driven mainly on the highway every day, 2x 20 km or 2x 28 km and during this time it only turned on the error P243C once, while on longer trips over 150 km (driven twice ) always turns on the same error p 43C. During that time, the car is running quite normally, except for the last time, when it was driving at a constant speed of 145 km/h, it simply did not want to accelerate any more. This lasted for 5-10 seconds and the car behaved quite normally after that.
The fuel consumption is high considering the data from the on-board computer and also when compared to the Mercedes GLA 200 D with 7 DTC (DSG) gearbox. Let me emphasize that the transmission ratios in the last gear are the same, ie 130 km/h is at 2250 rpm. Mercedes is a taller, larger car with more weight and bigger tires and a 50% bigger engine, and it would be logical that it consumes more fuel compared to the lighter and lower Mazda.
During all this time, the oil level in the engine has not changed. It's the same all the time and about 4000 km have been driven.
Most likely on Monday I will physically remove the DPF and close the EGR.
If someone has a better solution, please write. Thank you all.