The EIC "look back" certainly can be e-filed. I do not know of any issues with it.
I suggest contacting customer support to look at your issue.
There is no single published number because it changes contently depending on the nature of the call and agent availability. Following the link below will either give a current number for you to call or take your number for a callback.
(Note that phone support is for paying customers only. There is no phone support for Free Customers.)
Here is a TurboTax FAQ for contacting customer support.
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
