Old account got banned a couple of years ago but was never able to submit a case review?

Till 2015 you could have posted for clarifications in the xbox forums. Only from August 2015 there is the possibility to file for a case review from the xbox enforcement site, yet since your suspension marks over 12 months (the period within which you can
file for a case review) this is not possible anymore.

At this point there is nothing you can do since there is no possibility for license transfer from a suspended account.

I'm currently unable to submit a case review because the account was banned 6 years ago, so long ago there was no way to make a case review and I am unable to submit one now because the ban was given so long ago and the case review system I assume was
implemented recently. Is there any way this could be forwarded to the Enforcement Team?

The enforcement team does not use the forums and since the ban took place over 2 years ago, you would not be able to submit a case review. So there would be no way to get the account back.

The enforcement team are the only ones who handle suspensions/bannings. Submitting a case review is the only way to contact them, however, you cannot submit a review on any enforcement actions over 18 months old. Since you were banned 5 years ago it would
be too old for a review and at this point there would be nothing you can do.

Since it is an old account/ban you probably will not be able to find out any information on the specifics. It is too late to submit a case review and a permanent ban will not be reversed.