You call them 'The person I owe money to'
The presence of owing money is referred to as being 'in debt'. A person who is in debt is a debtor.
umm by phone or if the question is meant to be (waht do you call a person with a lot of money) that answer is rich
Poor
Flowing honey
A——T
spendthrift
a spendthrift
A borrower
Electrician!
smart
A payee.