c220 cdi 2012 se exec

[stassin2]

My car c220 cdi 2012, with 28k miles just had total engine failure. B service carried out by MB in may 2014 at 21k miles. MB saying I must pay £7.5k towards £13k repair as there is no evidence of the first service being carried out.
I bought the car with 18k miles in Dec 2013.

Any one heard if a similar situation or can advise how I progress.

Many thanks.