Having a bit of problem with a setup, i do not have much experience with telkom infrastructure

Currently i have a cisco 2921 with 2 VIC2 - BRI-NT/TE interfaces. This acts as my gateway/trunk for incoming and outgoing calls. I also have 4 lines hooking up into 4 telkom isdn2a network termination units.

My problem are as follows :-
-when using the supplied isdn bri cable (which looks like the crossover variant) no calls work at all.
-when using a straight through ethernet cable, i can make and recieve phonecalls but the audio is one way. I cannot hear what the guy on the outside is saying. This tells me that the config on the ciscos are ok.

An observation from me, all our other PRI lines come straight from a krone block and into our cisco routers via rj45 connections. Could i possibly need to do the same thing with the BRIs?

I have checked that both the router and asterisk supports g729.

Anyone have any ideas?