Very long delay waiting for a replacement

Tupperware provide a lifetime guarantee. I have been waiting since 1 October 2014 for a replacement of a cracked lid/seal for a cereal container. It is now 13 and a half months which I feel is extreme. Every time I check with the agent, she says not to worry, they haven't forgotten - there is just a backlog. Last year the story was that it was because of a worker strike.