I kind of use this phrase a lot when speaking Greek, and sometimes I feel the need to say it when speaking English as well but cannot think of a good candidate, as a non native English speaker, I also don't know if there is an English equivalent.
The phrase feels a bit slang-ish so I cannot think of a literal translation.
The usual usage of it is when you need to answer a question with a rhetorical question because you don't know the answer and you are in question as well. e.g.
A. The buses were on strike and I had to walk home.
B. Why didn't you call me? I could give you a ride.
A. Έλα ντε?
Free form translation could be something like "Yeah, why didn't I?"