overcharged

On 02 september I bought a few items including four 2meter lengths of 22mm Pvc conduit. When I arrived home I realised that I had been charged R-82.00 per length !!!!!! I immediately placed a query on the builders warehouse website but have to date received no response from them. The same pvc conduit is being advertised by Chamberlains for about R-12.00 per 2m length, how does Builders Warehouse manage to charge R-70.00 more per length? That is R-280.00 that I have been overcharged? Invoice number is C***