My phone sensors are not working and customer care personnel are sayin

My phone sensors are not working and customer care personnel are saying that it has caught water and motherboard needs to b changed and warranty is also void so need to purchase New motherboard for 12000 Indian Rs

I don't know how to see if other parts of phone are not damaged

Like display , camera , front cam, earphone , speaker etc.

Samsung care has not said any such thing till now they only said about motherboard to b replaced

now what should I do

I don't get it if it's water damage then why don't other thing of have not been affected

And what else can h reason for sensors not working

Or how to know if others hardware parts as I mentioned earlier like display etc. Or battery May have been affected

Is 12000 Rs Indian price justified for motherboard as i have read that this is the cost of display

Can I rely on services of engineer at Samsung care in my town that replacing this he won't make any mistake and if he does so than Will he tell me and if he don't what procedure should i follow

Thanks