Asterisk, mISDN, cant read DTMF codes coming from cell pohne

hi

my asterisk runs with misdn it accept calls, can play messages etc.
But i when i want it to read() a dtmf code sent from my cell phone
it always says:

    -- Executing [i@Extern1:5] Read("mISDN/1-u4", "NUMMER||4") in new stack
    -- Accepting a maximum of 4 digits.
    -- User entered nothing.
    -- Executing [i@Extern1:6] NoOp("mISDN/1-u4", "") in new stack

when i use my cell phone calling for example some support hotline using “push button 1 for technical support, button 2 for smoe other stuff” it always works. But i cant tell whether they use dtmf or some other technique.

in my misdn.conf file the only option i could find including “dtmf” was senddtmf=yes

does not show anything while trying to use dtmf.

what other configs do i have to check? or what other possibilities for interacting between my cell phone and the asterisk server do i have?