Club Factory Online Shopping App - Not all items delivered and returning the received items

It is almost two months i am suffering from mental agony. I had placed an order (SO*********) on *th April **** which included four items (* pair of shoes). I received the packet on **th April **** but there were only three items in the packet.I registered a complaint on **th April **** over the call (****-*******) about this missing item (Item no –MSC*********N). They suggested me to reach you via chatbox on mobile app. So, I did the same and explained
the problem.
I got assurance that they will fix this problem in next *-* working days. I followed up over * times (including call and through app) but found no resolution so far.I have attached the full chat history with a support guy for your reference.
Meanwhile, I wanted to return those * items which I received so far. But whenever I wanted to return it through app, it asked me to confirm the delivery of all * items which actually did not happen. So, I never accepted/confirmed it and hence not able to return it yet. And obviously I cannot confirm until it’s delivered.
I have already raised this problem to support guy. Also attached the chat for more information. Apart from chats, I also have a recorded calls I made to customer care in which I have mentioned these problems (in case you need them, i can provide).
So finally I have two problems now which needs to be addressed on priority –
*. I have not received an item (which I do not need anymore :-( )
*. I want to return those * received items which I cannot do because it’s asking for delivery confirmation for all four items first.