No one is in direct contact with the Imam (aj) and no one can guarantee a dua being answered. If a dua is answered or not depends on many conditions. You should strive to recite Dua Tawassul every Tuesday evening.

Also this dua

Eleventh: Shaykh Kaf`ami in his book al-Balad al-Amin has written, "This is the du`a of Imam Mahdi (`a) that he taught a person who was imprisoned. He was released, thanks to reciting this du`a.
إِلَهِي عَظُمَ الْبَلاَءُ وَ بَرِحَ الْخَفَاءُ وَ انْكَشَفَ الْغِطَاءُ وَ انْقَطَعَ الرَّجَاءُ وَ ضَاقَتِ الْأَرْضُ وَ مُنِعَتِ السَّمَاءُ
My Allaah, irretrievable is our plight, our helplessness causes pain and trouble, (now our) urgency has been laid bare (before Thee), (all) hopes have been cut off, the (plentiful) earth has shrunk (with very little to spare) for us, the heavenly blessings have been withheld,
وَ أَنْتَ الْمُسْتَعَانُ وَ إِلَيْكَ الْمُشْتَكَى وَ عَلَيْكَ الْمُعَوَّلُ فِي الشِّدَّةِ وَ الرَّخَاءِ
we call upon Thee for help, we refer our grief and sorrow to Thee, we have full faith in Thee, in the time of distress as well as in good fortune.
اللَّهُمَّ صَلِّ عَلَى مُحَمَّدٍ وَ آلِ مُحَمَّدٍ أُولِي الْأَمْرِ الَّذِينَ فَرَضْتَ عَلَيْنَا طَاعَتَهُمْ وَ عَرَّفْتَنَا بِذَلِكَ مَنْزِلَتَهُمْ
O Allaah, send blessings on Muhammad and on the children of Muhammad , the "Ulil Amr" (authority), obedience to whom has been made obligatory, through which their high status has been made known.
فَفَرِّجْ عَنَّا بِحَقِّهِمْ فَرَجاً عَاجِلاً قَرِيباً كَلَمْحِ الْبَصَرِ أَوْ هُوَ أَقْرَبُ
Therefore let there be joy after sorrow for us for their sake, right away, in the twinkle of an eye, more rapidly.
يَا مُحَمَّدُ يَا عَلِيُّ يَا عَلِيُّ يَا مُحَمَّدُ اكْفِيَانِي فَإِنَّكُمَا كَافِيَانِ وَ انْصُرَانِي فَإِنَّكُمَا نَاصِرَانِ
O Muhammad, O AIi, O Ali, O Muhammad, Give me enough, because both of you provide sufficiently, and help me, because both of you help and protect.
يَا مَوْلاَنَا يَا صَاحِبَ الزَّمَانِ الْغَوْثَ الْغَوْثَ الْغَوْثَ أَدْرِكْنِي أَدْرِكْنِي أَدْرِكْنِي
O Our Master, O the Authority of our times (Saahibaz Zamaan), Help! Help! Help! Come to my help! Come to my help! Come to my help!
السَّاعَةَ السَّاعَةَ السَّاعَةَ الْعَجَلَ الْعَجَلَ الْعَجَلَ يَا أَرْحَمَ الرَّاحِمِينَ بِحَقِّ مُحَمَّدٍ وَ آلِهِ الطَّاهِرِينَ
in this hour, in this hour, in this hour! Be quick, Be quick, Be quick! O the most Merciful, For the sake of Muhammad and his pure progeny.