dirty marks on 2 canvases & no one working day reply

I have used 1clickprint a lot and always been happy with the quality. But last week one of my canvases arrived with a dirty mark in the corner, spoiling the image. I emailed them about it and got their standard automated 'we will reply within one working day' email. After THREE days of NO REPLY I emailed them again - its now FIVE DAYS and NOTHING!

To make matters worse, today a much bigger canvas was delivered - and THAT has a bigger dirty mark on it! I feel badly let down and wonder if its worth me emailing them if they are not going to bother to reply. I am going to need either refunds or replacements. Such a shame as the QUALITY of their prints has, up until now, been better than anywhere else I have tried!