Trying to submit unpaid item case but it is only giving me the option that I have agreed to cancel transaction

Hi - First time question for me. Buyer bought item on 17/9 and contacted me to ask if I would wait for payment until he had bid on other items so that I could combine postage.  I agreed and asked him to contact me requesting total when he had finished. He bought another 2 items. As I had heard nothing by 16th October I sent invoice combining 3 items. I've heard nothing since- no response to messages. I have tried to open unpaid item case today but I'm unable to select 'unpaid item' option for the first item - it has automatically selected the 'agreed to cancel transaction'. The other 2 items give me both options. Would really appreciate advice. I tried separating the items into 3  invoices but made no difference. Would really appreciate advice.