As I stated above, you could've also logged in with an email / password. If you only ever played as a guest & can't recover your gane, you need to contact SUPPORT. https://portal.pixelfederation.com/en/diggysadventure/support
Scroll down for category options to begin the form.
You'll need your current Player ID# ( found under the Settings cog in the upper LEFT corner on Mobile, RT on PC.) Plus if you know your old game's ID#, that'll help them recover your progress. If you don't know it, give as much info as possible: level, device played on, any monetary purchases, etc.