called back with no tone , strange

Rang and when I answered the computer said goodbye

Answered call, seemingly no-one there, then after a pause a female voice said something but I couldn't understand what - really just a sound, then they hung up.

I answered and a computer said goodbye

Calls and then hangs up... Assuming scam

Caller: I don’t know

Rang my mobile and did not leave a message

they rang my landline. i did not answer and they did not leave a message.