Same here. I was trying to access Gumtree for the first time in a while and didn't realise until too late that I'd signed up to this. Not responding to emails either.
They call me endlessly, Sometimes twice a day. I think they are trying to sell bitcoins. I have asked them not to call me or contact me again, But it falls on deaf ears. I have put this number into BT, But that hasn't made any difference.