misleading payment info- pay within 20 days

Brought some clothes back in January for £52. Thought I had paid at purchase and just received a letter with two late fees. £14. I phoned up and apparently I clicked pay within 20 days. I was told people make this mistake,and sometimes click the wrong button but I couldn't receive a refund on late fees as I had agreed to it by clicking the wrong button. I couldn't pay there and then I have to go online and do a bank transfer. When I got my clothes I could have paid but I wasn't aware I hadn't. I got an email apparently amongst my spam about first fee and this is my reminder in letter format with another fee added..first I knew. Would have liked a letter separately with clear indication I hadn't paid. I now apparently have a credit black mark and late fees....Thanks H&M....So unimpressed with customer service. Never had this problem before with other stores and shopped online many times before but first time with H&M. Won't be shopping with them again...........