Problem with website and WHMCS

Hello, My website example.net is not working as getting Index of / error after placing a demo order which may cause of this issue, I have installed WordPress as front-end with WHMCS (example.net/my) and cPanel 34.196.xxx/.xx:2087/. The day before yesterday it was working as expected. When I placed a demo order, it was successfully placed and got the order number too but when I click on go to my account its started giving me 404 not found for all pages. Looking forward for your positive reply. Thank you for your great help. Uday.