Can't provide you any help, but you are not alone.
I am waiting for SEVEN flights to get credited to my account since early October this year.
I sent follow up e-mails regulary, but all I get in response is their generic reply like:

...Thank you for taking the time to contact Etihad Guest with your request for missing Etihad Guest Miles to be credited to your account.
The retro claim request is currently under process and the miles will be credited to your account subject to eligibility.
We look forward to welcoming you again as our guest in the future...

As you said, this is so annoying!
In the recent past, I realized I often questioned myself, if this hassle is worth to stay loyal to Etihad anymore...
The trouble and the time invest is not worth it anymore!
But hey, they look forward welcoming us again...?!?!