Hm , it sucks that you could only get a CI+ module and not a smartcard.
I have been experimenting with a Telenet setup "Teleent met een kaartje" where I had to use a CI-module as well as I couldn't get it work with Oscam.
For that I had a Terratec H7 with a CI-slot.
Just a stupid question: did you enable the ca0-slot in TVHeadend. By default it is disabled.
I assume you did, but just to be sure...
What is the status of the ca0 in Configuration->DVB Inputs -> TV Adapters?
IIRC it could have 3 states: ca0:disabled (default), ca0: empty, ca0: ready (or similar)
To get that Telenet-setup working, I had to add a fake CA-client.
Configuration -> CAs
Add
Type = CAPMT
Client name and Comment -> not important
Mode = OSCam (rev >= 9095)
Camd.socket file = /tmp/camd.socket
Listen/connect port = 9000
Without this fake (and unrelated) CA, I could not decrypt any channels at all.
Maybe you could give that a try?
I got my info here (https://tvheadend.org/issues/2794)
This way I got it working for the CI with the Telenet card, and without Oscam.
I don't have that setup anymore, so there's not much I can try at this moment...
Can you can try and see if this works for you?