Someone else answering my phone

[TDAnett]

Hello!
It has happened yesterday for the first Time. I have my O2 number for nearly 8 years. My husband was trying to call me and someone else answered , sounds like an indian guy, didn't say anything else apart of hello, hello, hello though..
I called- my number from a different number Than my husband's ,that was ok.

Does anyone have an idea what is happening?

[pgn]

Was your husband calling from his mobile or from an office land-line on a private switchboard, @TDAnett? 

[MI5]

@TDAnett 

Crossed lines are very rare now with digital networks but occasionally they do happen. 

More likely if maintenance is being carried out at the time too.