Last year I performed obligatory hajj and later I came to know that those who have dues of loan on them are not eligible for obligatory hajj. As I’ve due instalments of loan on me, would I have to perform obligatory hajj again? Whereas I had enough money to pay the complete loan amount and I, even, directed my son to pay these in case of mishappening.

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Yes, this is the ruling if you were able to pay the loan, it was better to pay before going and yes your son was able to gift you the expense of haj if he had performed his haj in past or had to go with you because one has the potential for haj first he has to perform his own wajib haj.
If in past you had the potentiality for haj and there was not any loan at that time and you were not gone for haj and now loan is due then still you have to go for haj because it was wajib and not performed.