I'm with the others....keep annoying them.
Demand a replacement be sent to you immediately!!! If you ask for a refund it will take them ages where as replacement would prove quicker and easier for them, if you annoy them enough you may get some extras to keep you off their case????
We have one of their thermos' and have had no trouble, that said if we did have trouble with it and we bought it locally I would take it back to the store for refund/replacement and let them deal with it.
Goodluck and keep us in the loop on how you get on.