Is it reasonable to ask property companies to provide formal invoices when paying property fees? Is it legal to refuse to pay the property fee without providing it?

Is a reasonable request. Property services are also business activities and should be invoiced. If not, you can report to the local taxation bureau. You should pay the fee first, and then issue the invoice. You can't refuse to pay the fee on this ground. Relevant laws and regulations,

Article 19 of the Measures for the Administration of Invoices in People's Republic of China (PRC): When units and individuals sell goods, provide services and engage in other business activities and collect money from outside, the payee shall issue invoices to the payer; Under special circumstances, the payer will issue an invoice to the payee.

Article 20 All units and individuals engaged in production and business activities shall ask the payee for invoices when they pay for goods, services and other business activities.