Hey @kiranbaby. We can organise a Post to Prepaid change for you, if there was any outstanding charges those would apply otherwise there should be no issue organising that change.
Please note that we’re unable to look into account details on Yes Crowd. We recommend messaging us via the My Optus app. Our Messaging team is available 24/7 and are ready to assist customers as quickly as possible. If for some reason you’re unable to use the My Optus app, please send a private message to the official Optus Facebook or Twitter page for further assistance.