I did some changes to make this work finally,
I setup a trunk with antisip credentials and another trunk with fairytel credentials The context in both cases were from-pstn and codecs were ulaw and alaw only. Later, I created two outbound routes.
One was called antisip-outbound and it has the dial pattern of fairytel in it (i.e) 479XXXXX and the trunks were in the order antisip and then fairytel. But, I think we don’t need antisip here. Then. I created another outbound route call fairytel-outbound which has the dial pattern of anti-sip (i.e) 431XXXXXXX. The trunks for this were fairytel first, then antisip.
Now, if I make a call from any extension, it knows if it should connect to the fairytel trunk or antisip trunk and makes the call correctly. This way, I got two different providers connected inside my freePBX.