Can a debt collecting agency free bank accounts?

A company called Buchananclark and Wells have told me that as I didn't defer my student loan (haven't earnt enough to pay it over the years; this debt is more than 6 years old) they have the power to freeze my bank accounts so I can't pay my bills and I will get in further debt, unless I pay them the entire loan. I said that that is just creating further debt, if it is true. I called his bluff, think it could be scare tactics but anyone know if there is any truth in it?