debt error

######app/models/debt.rb
#Calculates how long to pay off each debt in order of highest interest to lowest
  def self.payoff_highest_interest(debts)
    balance = debts.sort{|a, b| b.interest <=> a.interest}.first.balance
    date = Date.current.beginning_of_month
    debts.reduce(0) do |acc, debt|
      while debt.balance > 0
        date = date + 1.month
        acc + 1
        adj_bal = balance + debt.compound_interest
        if debt.user.payments.map(&:expected_on).include?(date) ## ERROR OCCURS HERE I THINK
          debt.balance = adj_bal - (calculating_debt_payment(debts) + debt.minimum_payment + debt.user.payments.where(:expected_on => date))
        else
          5.00 ## IGNORE THIS PART
        end
      end
    end
  end
  
  
  ######Server log
  Started GET "/users/1" for 127.0.0.1 at 2015-02-12 22:37:02 +1100
Processing by UsersController#show as HTML
  Parameters: {"id"=>"1"}
  User Load (0.3ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = $1 LIMIT 1  [["id", 1]]
  User Load (0.3ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = $1 LIMIT 1  [["id", 1]]
  Debt Load (15.3ms)  SELECT "debts".* FROM "debts"  WHERE "debts"."user_id" = $1  [["user_id", 1]]
  CACHE (0.0ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = $1 LIMIT 1  [["id", 1]]
  CACHE (0.0ms)  SELECT "debts".* FROM "debts"  WHERE "debts"."user_id" = $1  [["user_id", 1]]
  CACHE (0.0ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = $1 LIMIT 1  [["id", 1]]
  CACHE (0.0ms)  SELECT "debts".* FROM "debts"  WHERE "debts"."user_id" = $1  [["user_id", 1]]
  Payment Load (17.4ms)  SELECT "payments".* FROM "payments"  WHERE "payments"."user_id" = $1  [["user_id", 1]]