I paid the property management fee three years ago, and now I have received a letter from my lawyer asking for a receipt. If not, is it reasonable?

Hello, it's unreasonable, but the law needs to rely on evidence. If you did pay the legal fees, you can find the collection voucher and transfer record at that time. If there is no written evidence, see if there are any witnesses present to testify. In short, you need all the evidence that can confirm your statement.