We have a scanpan classic 28cm 5 litre saucepot that we've had about 5 months. We had another previously, which had pitting around the outside after only a few uses and it was swapped over for this one we now have. It was fantastic for a few months but now EVERYTHING sticks to it. Unless something is literally shallow frying things stick to it like glue, it's a pain to clean and it's really annoying. Any advise? Or is just a case of take it to the store and prey they swap it over again?