Refuse a refund

I bought an Avent therma bag on the 2nd of July 2015 , i started using on the 5th on Sunday . i made a bottle at 9am put it in the bag before going to church at 11am when i was about to feed my baby the bottle was cold , i tried again at home in the evening same story the bottle was cold , on Monday the 6th i returned the bag off course because i used it and it was light blue there a small part of it where it was dirty.They told the could not refund me because it is dirty then they phoned AVENT consultant who promised to come on the 8th or 9th to test the bag, on the 9th i received a call from the consultant telling me she is busy she couldn't't come and she ask me to go to the store to do the test or wait for her till she comes on the 14th or the 15th , the shop and the consultant they are not only inconveniencing me they are also waisting my time and costing me a lot of money because to go there i must pour in petrol. please help