NGT LITE

Has anyone had problems with this app?  I have installed on my mobile phone but I am unable to link my landline number only my mobile number. I have contacted NGT and am following their instructions to the letter but the landline will just not link - I get a message in the app stating ' link failed-retry'.  My landline phone provider Utility warehouse confirm that that they are compatible with local loop unbundling. Now NGT say it must be the phone number that is the problem. I am going from one to the other with no solution.