Inferior Chromodek Sheeting from Tilley Steel

Strongly advise against purchasing chromodeck sheet from Tilley Steel in Queensburgh (Durban). They are sold me inferior material (sheeting). Chromodeck normally has a 10 year warranty. Structure installed less than 3 years ago and sheeting is fully rusted on top side. I contacted them, they said do to my location from the sea... I am on the Bluff and I am at least 5km from the sea. I have another awning structure that was installed one year before using chromodeck from another supplier and those sheets are still as good as new. Therefore that is the bases for me stating that their material is inferior.