Please be more precise. You can normally get the bill after contractor came and clean your aircon. So, i don't understand the purpose of this thread

First of all, check your tenancy agreement. Sometimes, the landlord can hold the utility deposit up to one month after your departure to settle any outstanding payment.

If there is no such clause, then you can ask the landlord when the contractor told her that the bill will be issued. If she say don't know, ask the contractor number under the pretense that you want to push for it as you need the money.