Could use help with port forwarding a DS-Lite connection

Hi guys,

i got a server with Owncloud running now and i want to set it online.
I already used port forwarding a few years ago but not it just dont work.

I got a crappy FritzBox and at the support site it tells me port forwarding will not work with a DS-Lite connection and guess what: I have one of these connections.

At one site there was the hint that i will work with a relay server and most of the NAS manufacturer will give you access to this service for their products. Because i am using my own build, this is is not an option for me and i am not that deep into ipv6 magic. Can anyone help me please set my OwnCloud server online? Of course i am searching for a free, or quite free (about 20 bucks a year) solution for this problem.

(I could give you 50GB or even more if you want to and promiss not to do something illegal)

greetings from germany

Felix