Stop spam calls

The call's have been coming regularly and we're listed as 'suspected scam' but when it rang again just now, the scam warning had been removed and I called it back. I was on hold to just random music until the woman said hello, and that it had been a courtesy call from Vodafone calling to thank me for being a pay as you go customer and what do I use my sim for?? I said thanks but I don't really have time and her reaction gave the game away. She said she'd call back but I have since checked the nu