Suggestions for a Point-to-Point reliable Wireless Communication Module
You ask about the Xbee-Pro 900.



As the name suggests this works in the 900 MHz. The datasheet mentions a LoS range of 3 km, but since you don't have LoS that may be considerably less. The module has an RF connector, though, so you can connect an external high-gain antenna, which, again according to the datasheet, would increase the range to 10 km LoS. Should be enough for your application.  

Your link is to an eBay reference. I wouldn't buy from sources like that. For Sri Lanka Digi has a distributor in India, which will probably give you better support. (Many product you buy on eBay you can't get any support for at all.)

Further reading
Xbee-Pro 900 Manual