@ Sequana why would we sell a theme which will clean/remove a customer website? It makes no sense. Probably your hosting company made a mistake and you should ask a refund from them. We provide a reliable product and if someone or you installed it incorecctly (removed something on your website), it’s not our mistake. At least, you could provide us your wp admin login and FTP login and we can have a look what happend actually, maybe nothing has been removed.
@ Harvey are you the one who install the theme for them? Have you seen the error? Are you an experienced developer? If yes, please point us to the details and we will take care.