If you have the oil pressure light on, you are in serious engine problems.
You can reset the service indicator but this is not linked to the oil pressure light.
Your best bet will be to measure the oil pressure:
https://www.google.com/search?client=firefox-b-d&q=measure+engine+oil+pressure#kpvalbx=1There is a very high chance that the oil pick up has been blocked.
Your engine sounds like before but this may not last for too long if it runs with limited oil circulation.
Diesel engines need frequent oil changes and these Mazda engines have a bad reputation on leaking fuel through the injector and then tarring the oil blocking the oil circulation.
The 12.5k miles oil change interval may be too long even without any problems from the injectors.
Mazda Australia service intervals are advertised as half the mileage compared to Mazda UK and while you can blame the dust and the heat, maybe more frequent oil changes could help UK cars from being scrapped too early.