Dear AlessandroBozzaotra
For all questions regarding the setup and operation of the tracker, it is best to contact the manufacturer or seller of the tracker directly; they are the ones who have passed the necessary competence to consider the issue.
You can also try to check whether the SIM card inserted into the tracker is set to receive phone calls, not just SMS, as well as the tracker’s operating mode. Perhaps it is configured in such a way that when a call is made from your phone, the tracker is blocked.