I bought 2 collars and put them on my dogs and kept waiting for the fleas to die but it never happened in the meantime I'm having to bathe my dogs every 3days to kill fleas. I eventually went and bought 2 more collars and I've waited 2weeks and still no dead fleas i've spent over $230.00 for 4 collars I got them at Walmart. My sister just bought them for her dog and her fleas are already dead. Who can I contact to demand a refund?