Ok, i don't know if in Spain, but, in Colombia we use this:
Se fueron sin pagar, ¿puedes creerlo?
Or you can use:
¿Puedes creerlo? ¡Se fueron sin pagar!
In this case you don't need some interjection, only translate literal and sounds good and grammatically is correct.
But, if you want user an interjection with
¿Puedes creer que se fueron sin pagar?
In addition, a very important advice, in Spanish you don't need to put the user explicitly in tenses: you can say something without the personal pronoun I, YOU, ..., etc., and everyone will understand you if you conjugate the verb properly, so, you don't need use
¿Te lo puedes creer?
Instead you can use
¿Puedes creer -lo?
Thin kind of sentences have a noun, pasive tenses, i can't remember good, but, using this you change
te lo with
verb + lo, for example.