Appeal against ex parte divorce decree

As rightly mentioned above, audio is not substantial proof.  

Secondly, the appeal period is not 30 days but 90 days as recently held by a Full Bench of the Bombay High Court. However, the same is not applicable in your case, as your wife will first have to move an Application for setting aside ex-parte Decree before the same Court which passed the ex-parte Decree within a period of 30 days from the date of knowledge. 

Despite having produced proof of delivery, the Courts will most likely condone the Delay and allow her to fight the case on merits.  And anyways, that is much better position for you as an ex-parte Divorce is like a sword hanging over the head.