:salamext:
Try to allow them to soak it in, sometimes you might call to something but the person might not trust your source because they're unsure where you're getting your info. from.
So give it time, infact - work harder on allowing them to trust you, then they'll trust you and where you get your sources from, and then insha Allah they will accept your advice.
I found it hard to tell some people that something wasn't allowed, that's because they never really trusted where i got the information from. Once i started telling them things
they did know, and enhancing on that (in matters of loving the Prophet sal Allahu alaihi wasalam etc.) - they started realising that what i'm saying is really from reliable sources, which gradually allowed them to trust me and what i mention.
So it takes time, patience, and trust. Give them the good that they already know with extras first, then gradually they will like to hear from you if you do it in a good way - then you can explain how what you've been saying is also from the same reliable source, so they should accept it, the same way they accept all that they agreed with beforehand. Explaining to them that we are not allowed to pick and choose based on our own personal desires in the religion, but we have to accept it all. And you just want what's best for them.
Remember that Allah says (translation of the meaning):
And by the Mercy of Allâh, you dealt with them gently. And had you been severe and harsh*hearted, they would have broken away from about you; so pass over (their faults), and ask (Allâh's) Forgiveness for them; and consult them in the affairs. Then when you have taken a decision, put your trust in Allâh, certainly, Allâh loves those who put their trust (in Him). (Qur'an 3: 159)
