Cann't Connect to Internet with iTune

Hi there,

Last 3 months ago I have owned iPad than I use iCloud backup option with my wife apple ID, but yesterday I got one message on our iPad. The message is This iPad hasn't been backed up in 13 weeks. Backup's happen when this iPad is plugged in, locked, and connection to WFi. I adready contact with iTune and backup when I got this message but message is not gone. Please do advice for me what should I have need to do.