Echo cancellation using digital audio path

Has somebody experienced problems with echo cancelation when digital audio path is been used (PCM) for input and output audio? A strong echo on a remote telephone is heard. I’ve tried to activate either the AEC (AT*EAUD=1,301,1), or Full Duplex Speaker (AT*EAUD=1,311,1), but remote echo remain strong with AEC=1 & FD_Enable=0. Whether AEC=0 & FD_Enable=1, the microphone signal isn’t sent.
The circuit block diagram I’ve using is the following:

Please, some idea? What I’m doing wrong? :frowning: