Hi there, anon service charge person here with a little bit of advice that might clarify this situation hypothetically.
The evidence / proof issue may well be to do with the type of service charge the homeoweners are liable to pay. They will be charged what is called a "Variable Service Charge" which has certain (legal) requirements to evidence the charge and they can ask to see historic accounts which are in most instances approved by chatered accountants. If your housing provider does not operate a variable service charge for its rented residents it may be that they do not have the necessary evidence due under a variable charge. Therefore, if they are looking to correct this sitaution to evidence the charge they will be preparing financial information to meet these requirements before they can start to recover their costs.
i have assumed you are not charged a variable service charge (to fit with this hypothetical answer) however, it is always worth checking your tenancy agreement to try and understand what type of service charge is in place. A Variable charge would either be stated as a variable charge or make reference to "actual costs", alternatively you could be charged what is known as a Fixed Service charge or even a pooled service charge. I won't go into the details of precisely what defines these charges, but in answer to your question the evidence required under these charges is not the same as those needed under a variable charge. Your housing provider shoudl be able to provide a service charge budget for the current year, which would show anticipated and know costs that they are going to incur in providing the services, they may even be able to provide details of last years spend on services to evidence the reasonableness of charge.
You reference "estate charge", more detail on what this means should be available so you can understand what services are provided / covered.
2 disclaimers -
1 - I have only pointed out a hypothetical scenario where this could occur .
2 please do not take this commentary as being a negative for fixed charges, I support social landlords using fixed service charges as they are far less expensive to administer and any money saved in the provision of social housing is clearly a good thing. Also a fixed charge that is well run is a perfectly fair way to charge for serivces.
I hope this helps, I'll keep an eye on the thread if any further general advice is needed.