I see, some information about IuUP certainly wouldn't hurt, for the good of all of us.
Also, you need to set up external MNCC. Your mail hints osmo-sip-connector, so I assume you're doing that, but if you're not seeing *any* packages to/from SIP, then your MSC might still be doing internal MNCC.
Is there anything else to do other than the -M flag? And to clarify, SIP works normally, even the DTMF signals go through, it's just the RTP packets that are missing.
Regards,
Pierre