MBFS useless service, cannot get a response

It has taken over a month for MBFS to respond to a simple enquiry and settlement at the end of their Argility finance. We have written emails, called them, visited TWO dealerships (who refer us back to MBFS), and when we do get a mail it is "encrypted" with instructions to "register with webmail" which do not work - repeatedly. This is actually "business on a plate" for you with an excellent client who has never missed a payment in over a decade! How about just picking up the phone and talking to your client - we have bought 4 Mercs in a row. This will most likely be our last engagement with Merc. Shame on you.