Pathetic service

I ordered 2 pairs of sandals for my husband, South African size 12 but we were sent a 13, we have tried since 2 December to get hold of them for an exchange but have not received any responses. When calling they head office or online services no-one bothers to answer the phone. We are no sitting with 2 pairs of shoes that my husband can’t wear. What are we supposed to do now. Absolutely pathetic service.