After pressing any key (sending DTMF) i hear "busy" signal

You will probably need to contact Openvox, or their reseller.

I can’t see any indication in the trace that Asterisk would terminate the call. I’m not 100% sure that the digits are being forwarded with a non-zero duration, but I doubt there is anything wrong there, as it would affect too many people. In any case, if the digits weren’t forwarded, there would be no busy tone from the far end, as it wouldn’t know you had done anything.

Your verbosity level isn’t high enough to see how Asterisk is handling the call, and you haven’t provided the relevant dial plan.

The correct forum for such questions when you wrote the dialplan yourself, is Asterisk Support. This is not a support forum.