Praise be to Allah.

Firstly: 

We ask Allah, may He be exalted, to forgive you and pardon you for what you have done, for riba is a major sin, concerning which there are warnings such as have not been issued with regard to other sins. Allah, may He be exalted, says (interpretation of the meaning):

“O you who believe! Fear Allah and give up what remains (due to you) from Ribaa (from now onward) if you are (really) believers.

279. And if you do not do it, then take a notice of war from Allah and His Messenger”

[al-Baqarah 2:278-279]. 

It was narrated that Jaabir (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) cursed the one who consumes riba and the one who pays it, the one who writes it down and the two who witness it, and he said: they are all the same.

Narrated by Muslim (1598). 

For more information on the warning to the one who deals in riba, please see the answers to questions no. 60185 and 141948. 

Secondly: 

If you have repented from this riba-based transaction and have resolved not to do it again, and you regret having done it, but it is not possible to avoid paying this interest because the system obliges you to repay loans with interest, then there is no reason why your relative should not help you to pay off this debt, and there is no sin on him in doing so, because that comes under the heading of relieving your distress. The Prophet (blessings and peace of Allah be upon him) said: “Whoever relieves a Muslim of distress, Allah will relieve him of distress on the Day of Resurrection.” Narrated by al-Bukhaari (2442) and Muslim (2580). Moreover, the longer your repayment of the debt is delayed, the more the interest that you owe will accumulate. As for helping one who has repented to pay off debt, there is nothing wrong with that, and it does not come under the heading of helping in committing evil in any way whatsoever, so the one who wants to help may give some of his zakaah to the debtor, if the latter does not have wealth surplus to his needs with which to pay off his debt. 

The scholars have stated that if one who got into debt for a haraam purpose has repented to Allah, there is nothing wrong with giving him zakaah funds  with which to pay off his debt. 

Shaykh Muhammad ibn ‘Uthaymeen (may Allah have mercy on him) said: 

Question: if a person gets into debt for a haraam purpose, can we give him zakaah?

Answer: if he has repented, we may give him (zakaah funds), otherwise we may not, because in that case it is helping in something haraam. In that case, if we give him he will go into debt again.

End quote from ash-Sharh al-Mumti‘ (6/235) 

Dr. ‘Umar Sulaymaan al-Ashqar said: If a person takes out a riba-based loan, it is not permissible to pay off his debt from zakaah funds aimed at helping debtors, unless he repents from having dealt in riba.

End quote from Abhaath an-Nadwah al-Khaamisah li Qadaayaa az-Zakaah al-Mu‘aasirah (p. 210) 

And Allah knows best.