Okay.
The subsidiary rules for class S are hard to understand.
Reading them they seem to state that income below 7500 euro per year could be subsidiary, but then extra complications are added in. The wording in the guidelines is confusing.
You should appeal the 65s benefit decision and also apply for Jobseeks Benefit Self employed the rate for this is the same as 65s benefit when you are aged over 65.
If none of this works and if you had previous class A employment before the year of your 63rd birthday, you could try asking DSP to fill in your 63rd year with class A credits.
It is allowable to claim class A credits in any year where you are also paying class S contributions. You could say you were not aware that you were entitled to claim class A credits at that time.
If you succeeded in this approach you could then possibly qualify under class A rules.
Your rental income would definitely be subsidiary under class A rules.
I know of other people who have succeeded in getting backdated class A credits.