Good news @ajn. Come to think about it no you shouldn’t be charged fora courtesy car on mb and something I was always provided by the dealer although they did try to charge me £1o insurance once that needed correcting. During the pandemic and not sure if it applies now or was a dealer specific charge, they jumped on the bandwagon just like hairdressers and were charging £25 sterilisation fee so got a hire car from mb. I can not see it applying now though.
Hope you get it sorted pronto for you.