Ackermans

My husband being harassed by Ackermans collections for outstanding money someone else. 13 phone calls yesterday alone, when he tells them this is his number registered to his name they slam the phone down just to phone ten minutes later again. We phoned Ackermans and they informed us that they cannot track his number we need to give them the account holders name , how do they expect us to know the persons name ???? Today again 5 calls so far, they phone till after 6 in the evening so know we will be getting more calls.