called but no message left

Rang my mobile.
Claimed to be charity but voiced by a recording of a woman's voice. Responded vaguely to my questions. Obviously a robot or mechanical Turk.

Rang landline twice today, rang off without leaving message

Has rung at least 6 times in the last 2 weeks and today left a blank/empty 11 sec voice message. Blocking the number now, sick of the calls.

Rang off after only a few rings. No message. Robot?

Rang on landline long enough to be transferred to my mobile then eventually rang off without leaving a message.

Rang on landline long enough to to be diverted to my mobile but rang off without leaving a message.