The spread sheet program "matching network calculator" which is available for free on
this page:

http://www.rfshop.co.uk/blog/downloads
can do what you need.

For example, it will convert the reflection coefficient

Mag =0.35 Angle = 78 degs , in a 50 ohm system, into an impedance of :

Z=44.91+j35.04
ohms

Does that sound like the right answer?

Incidentally, the program
uses the same equation you mention. Maybe your problem was in the manipulation of complex
numbers?