The actual call is made by a robot. The assumption is that many/most calls won’t get answered, so they don’t have to waste a human doing this: the human only gets passed the call when the robot determines that the phone has actually been answered.
The number of humans available is based on the proportion of calls that actually get answered.
What you are experiencing is too many calls being answered: the robot dials a number, gets an answer (you), but has no free human to pass the call to. The call is just dropped.
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