let my motor plan do what its supposed to do to fix my car please

Im super stressful with the service im receiving from mercedes constantia. I got a warning message last week on the car that i must top up coolant. i drove to the nearest garage and poured coolant and the error dissapeared. drove the car to work. on my way back from work, the warning message came back. i stopped again by the garage to add coolant then drove home. the following morning on my way to work, the message came back and i immediately called mercedes constantia to notify them of the error and that i would like to book the car. my booking was confirmed for monday 3 June but was advise to pass by on friday so they can check maybe its a minor issue. drove to merc constantia on friday 31 May but on my way there, the car switched off on me and i got stuck by freeway next to 14 avenue offramp. called merc to assist and AA came through to tow the car to merc. on tuesday 4th June, Nigel called me to tell me that they working on the car to determine the issue. wednesday 5th June he calls me to tell me that the engine overheated and the technical team says my motor plan would not cover this cost as the warning light was ignored by me. i have been back and forth with Nigel to understand how i must pay to fix the engine whereas im covered on my motor plan and that as soon as the warning came through on my side, i reached out to them for help and that constantia has been servising my car for all this years and they also couldnt fix the issue everytime they service the car. my car was with them few months ago and they never pick up that theres issue on coolant but kept on telling me that all is well with the car. now im strunded with no car while my car is packed at mercedes with no one taking my issue as important instead im being told they escalated the matter to the technical department to give way forward. ive been a loyal merc customers for years and never gave them an issues but now they dont want to fix my car while i took measures as soon as the error came through to try and fix it. i even spoke to Dan ( service manager) to see what can he do. i have motor plan which is supposed to help fix my problem but mercedes wants to punish me for an error that they also missed on their side cos how do you service a car for all this years and never pick up an issue of the coolant. i cant be kept to suffer carless and still be expected to pay to fix engine while ive got cover for it. can for once mercedes take accountability and give customers service to their loyal customers. now im waiting for the technical team which i dont even know if they exist or not to tell me if they will fix my car. im reaching out to whoever is incharge of merc constancia to please hear my cry and do what is right for your customers. can you allow my motor plan to do the job for me so my car can be fixed. im already suffering having to travel back and forth using taxis while im paying a lot on a car that is currently parked at merc with no one fixing it.