Multiple calls a day don't know who it is. Either silent or hang up

I could never understand what they were saying when they said the name, just got a call today, something along the lines of bag in offer? Not sure but its always about some electricity and energy bill i seem to have seeing as they call me about it, not certain if just telemarketing or a scam but its annoying

Have received 3 calls from them today, no Vmail left. Unsure of who this is.

Called number back and it says "number not in service"?

Have received several calls from this same number to my mobile, so in frustration answered the most recent one today ... soon as I heard the accent I knew it was a telemarketer so hung and have now blocked this number ... blasted nuisances and I'm on the DNC Register (which is next to useless!)

Have no idea who this is, have received half a dozen calls still don't know it is

hang up when answered