Advantis do not buy debt. I have used them in a past life to collect grossly overdue payments and found them to be very professional. They work for commercial concerns and that includes a large number of national companies.

They normally made contact by letter, possibly email these days, explaining who their client was and what was owed. There are, if the debt is to be dealt with anumber of ways to resolve the issue. Firstly if it is your debt...pay up. If the debt is not correct contact the people who are their clients as only they can call them of if the debt remains. Merely saying that you have no debt or that it is a mistake will have no credence with them. They will pursue the debt until paid or called off by their clients, I have never had any experience of them starting the process by telephoning a debtor.