TakeAlot returns issue

I ordered a Mellerware - LED Crystal Plate Capri Induction Cooker set from Take Alot. I received the unit on the Monday and by the Thursday the unit was no longer working. I logged a return/exchange with take alot (RRN-a4ff-57e8) The faulty unit was collected by one of their drivers. Now they have sent their drivers on 3 different occasions to collect the same return, this morning their driver Aubrey was here to deliver my new unit but refused to give it to me saying I had not returned the fault unit yet.I phoned Hatfield Take Alot offices while he was here and spoke to Beauty. She said that they use another courier company for collections as well, and she suspected that they had not handed the unit over to Take Alot's main returns center yet. I told her its the 4th time they are trying to collect a unit they already collected .They just took the new unit back, and i am now sitting without something I have paid for already. I am getting very close to cancelling the order and demanding a refund.....I am sick of fighting over this. I am disgusted with the lack of organization on Take alots side.Why did they not make proper queries into where the unit is with the collection company the first time I told them it was collected? Its not my fault that the other courier company is not doing their job. Also kindly take not that the returns status for the return of the faulty unit says "return concluded"