I've been looking into shoe returns myself for an unrelated reason. Your contract is with the place you purchased them from. If it was a shop then you may be lucky and find that they'll exchange them there and then. If you purchased online then you'll have to send them back and the wait could be up to 12 weeks (as in my situation).

Either way you should be able to run more than that before a shoe falls apart so they can be classed as faulty.

Alternatively, glue them back down.