As the others have said above, it may be simply a staffing issue, lots of dealer staff, backroom and sales, are furloughed. You don’t say how much the deposit was, or what did it cover, was it to cover extras, which may be a problem. I don’t go more than £500 on extras, and tend not to add them at all. I would get on the phone to MB, and explain, that the deposit has not been returned, and ask them to give the dealer a nudge. I would also phone the dealer, and get an update on the situation, and then explain, if its not returned by the end of this week, you have no option but to request a charge back, from the card company, if paid by card, and see if that kicks them into action.
On deposits, I have no problem with them, pay by card, so you have some protection, it also shows commitment to the order, and gives you leverage, when phoning up, and getting updates, and may help in getting money off the AP.