Combined shipping not working

We have been contacted by a customer re listing; 5787129684 saying that our FREE shipping offer when purchasing 3 or more items is not working.

We checked the listing and found that we had not ticked the appropriate box. We corrected this and 'updated' the listing. We then tested it by purchasing three items (P247848539) which we paid for using our credit card / Ping and found that the listing still charging the freight. 

It seems that there is a fault with combined shipping?