Phone calls rejected automatically from a specific contact

I have a Redmi Note 7 phone, from Xiaomi. Since some time, one specific contact cannot call me directly. Phone calls are automatically dropped and I only get a notification of a lost call. I can call him, but he cannot call me. I checked and this contact is not in the block list and I tried to remove the phone permission from all apps, but still, the contact cannot call me (so it is not actively blocked by an app). How can I solve the problem?