Invoicing for work not done

I had my car in for a service at Produkta Nissan in Nelspruit on Jan 5, 2018. On Sunday the 7th my son opened the bonnet to look at something and noticed that one of the plastic covers was loose as well as the plastic that holds the air filter. He opened the cover and told me that the air filter has not been replaced. We went back to the dealer and asked when the air filter was replaced and was told it was done on the last service. Upon confronting them with the facts, they suddenly changed their story and said they would have called us once they receive the air filter as they don't have stock. Not ONCE did they call us on the day of the service to tell me that they do not have stock, neither mentioned anything when i picked up the vehicle. The most shocking is that they invoiced for an air filter. For all I know, the fuel filter wasn't even replaced because if the bonnet was opened, the technician would have seen that all the covers are loose. They also didn't do a diagnostic on the vehicle because if they did, they would have seen that one of the glow plugs is faulty and also that the EGR is blocked and that one of the rear brake lights are not working. This is totally unacceptable and I don't even want to know with how many people they have done this, invoice for things that hasn't been done and then pocketing the money. The service manager also didn't seem to care when I brought it under his attention. They told me that the air filter will be in stock on the 17th of January.