This is a painful story to read. I have a 5DII being delivered for the the past six months myself, so I know how frustrated you must be.
this is eyactly what happend, thanks for translation my babbeling...only that both leaf and the dealer had promised I would get back my paid leasing rates, which didn't happen...
You were wasting your time talking to your dealer or Leaf about money. The camera belongs to the leasing company. It's unclear whether you got out of the contract already. In case you didn't, here goes:
As a finance monkey myself* having dealt with these kinds of cases, you have to talk to them on the terms they understand. Money. Tally up how much you have paid them already. Add up how much they received from the refund, if they received one. The difference between the two is how much he made without lifting a finger (minus overhead and some misc costs).
Say to him "You've made X euro off me in Y months, most of it pure margin. [then the bit which matters:]
The next time I purchase a big ticket camera system why would I use your leasing company if you don't reason with me now, and let me out of the contract. Win-win." Reason with him
on his terms: revenue and margin.
If reasoning doesn't help, mention small claims court or whatever you have in Germany for these cases, but don't threaten - just say that that is an option you might need to take to protect your business. A finance monkey knows that the margins he's made from you will quickly disappear down the maws of trained attack lawyers, no matter what the outcome of the court case, and wastes his time he would be better off making new contracts.
Alternatively, go back to your leasing contract. Read it over carefully. There are rules on how you can get out of the contract - they are probably quite unfavorable to you, but there are certainly contractual ways. If there isn't an acceptable method, contact the German trade association for such companies for advice.
* this is not professional advice, usual disclaimers, IANAL etc. don't sue me please