Avoiding repair under maintenance plan

Our Smart car would not start and on tow away we discovered it is flooded with water under the front mats, at least 1 cm deep in water. An L-bend pipe was lying loose under the carpet. Technician quoted +/- R14000 for repairs to a unit that sustained \prolonged\" water damage. Every time I challenged their findings and reasons for the water leak their reasoning changed. Is it a Mercedes KPI for technicians to find reasons and excuses that repairs is not covered by motor plans and guarantees? The latest reason for the flooding is that we tampered with the car battery, loosening the terminals and some how knocked out the L-bend overflow of the Air Con. Car has only done 12000 km and still has the original factory fitted battery. I am a single mother and the Smart Car is my 24 year old daughters car. I am a professional in the FMCG manufacturing industry and my daughter is a Masters student. We do not spend our time tampering with car engines and batteries. So do not be under the illusion that because your car is under maintenance plan you are secure, Mercedes will FIND a reason for you to pay for repairs."