Not upholding guarantee

Purchased Shogun knives from Verimark with a lifetime guarantee. Knives have almost all broken (blades break off). Staff member refused to help at all with a very bad attitude. Manager eventually agreed to replace the knife. I have now been to collect the knife (having left my knife at the shop) three times and the rude staff member refuses to assist. He insists that I visit during the week and not over the weekends, but I work!!