My partner and i have recently bought a West highland terrier, he is 13 weeks old!?

we are finding it hard to toilet train him, we he does the toilet on the news paper we take him out to the back garden, and we also take him for regular walks!! Yet still no luck! we live in a flat which makes it harder! When we go out he will hold his toilet in and not do it in his area ( which is common for dogs) but also when we are at home he will hold his no 2's until later on at night even though he has been took out for walks!! A relative has advised me that he has probably been newspaper trained for too long, although this was great wen we first got him! We have had him two weeks now... has anyone got any suggestions for us ?? Help please !! Thank x