I receive up to 5 daily unknown callers who do not respond when i answer the call. This has been going on for many weeks, perhaps months. the numbers are all similar but few are the same number but the behaviour is the same. The caller listens to my response to the call for as long as i do not hang up. Sometimes the caller hangs up within a minute. If I do not answer the call with abut 30 seconds of the call tone, the call hangs up.