whatsapp not registering


I live in UAE. I just insatlled 4.4 Custom rom on galaxy s2 gti9100 and reset everything. My Airtel sim is still workking here. I can recieve calls and messages but I cant register my whatsapp. I was able register once after flashing rom then i tried flashing another rom and reset again. Now i'm not able to register whastapp.
somebody help please.
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