So I have Samsung Galaxy S3 Neo I9301I and the only time there was a 3G internet was for one second at a place where you could barely connect to internet. So do you know thy is it not working?
Unfortunately that phone is not suitable for use in Lithuania. It can't handle the frequencies used by Tele2 or the other 3 carriers. Best thing to do is sell it on Ebay and purchase a compatible phone. Before you buy anything check out your proposed purchase on WillMyPhoneWork.net - Check if your phone works on a network to make sure it will work.