Notes in old currency collected by Paul and mum (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

[ O(abbrev. for “old”) RAND(basic currency unit of South Africa) ] contained in ( collected by ) [ ME(Paul, this crossword’s setter, using the self-referential pronoun) + MA(a familiar term of address for one’s mother/mum).