I've made app that allows me to connect to bluetooth le device and lists all services and characteristics. However the only recognized service is 'Device Information Service', there is also 'Unknown Service' but it doesn't seem to pass data that im looking for. I'm sure that device is working properly because official app that was attached to the device works fine. What could be the problem? Is it possible that information that im looking for are passed in unknown service and are somehow encrypted?
Your app correctly discovers the services, the problem isn't there. The problem is that you expect the service to be a generic one but it isn't, it's a vendor specific service.
A vendor specific service (characteristic) is easily recognizable : Its UUID is 128 bits long. Also it's not resolved by generic BLE apps such as nRF Connect for the simple reason that they are specific and not generic.
When a company sells a device that implements generic services, they know that it will work with multiple applications but they also know that these applications will also work for the other devices from their competitors. By example, you can buy a heartrate belt from several companies and use them with several fitness apps on your smartphone.
When a company sells a device that implements vendor specific services, they know that it will not work with another application than their own one and that not any competitor will be able to sell a device that also works with their application.
Two different strategies, many different goals.
Basically, the company that designed the device you are playing with did not want you to be able to use another app than their own app to access the data in the device. It's that simple.
Now you still can reverse engineer their service. Use a sniffer, compare the data transferred when using their app with the data actually displayed in the app and maybe you'll find some logic, and learn the hard way how they have hidden the data in their service. However they probably have some clause stating you shall not reverse engineer this or that.
You can see the generic services here, but you won't learn anything more than what I've said : BLE GATT Services