Anyone else noticed quick late payment letters for fashionworkd/marisota ?

lots29

Hi - not sure if this is just me and I am genuinely flying close to wind, but I have a coupld of online accounts with 2 clothes companies. When I get my post statement I always go online to pay before the deadline and for the last 4 months this payments seems to trigger a letter from them saying I am late with payment and casued a £12 charge........I know they take 10 days to process but I just wondered if anyone else has noticed this payment triggers late letter phenomenon ? !