don't leave a message. when I tried to call back - voice says number is disconected

Mumbling in background.... didn’t leave any message

This number has come up on my phone a few times. I did not answer because I do not know this number..
Today I answered the call, but said nothing and had it on loud speaker.
You could hear many voices in the back ground and it a while for the ( person ) to say hi.
After one or two ‘hellos’.... the phone call ended.
Yes obviously a call centre of some sort

4 calls over 2 days
dont leave a message except the last time by accident by the sounds of it as all you can hear is people talking in the background