Who has responsibility for repairs will depend on the lease.
Generally the building owner/freeholder retains responsibility for repairs to the external /structural parts and common parts. The costs/expenses incurred are then, generally, passed on to the tenant via a service charge.
However, the freeholder could have passed the repairing obligation on to the council if the freeholder has let the whole property to the council.
You can search the land registry to find the registers of title to the property. The lease could well be registered / noted on the title. If so you can purchase it for approx £3 per document. You can then check who has responsibility to repair. If the freeholder, you will not have a direct contractual relationship and have no legal right to demand repairs, this can only be done by the tenant, I.e the council. Do check your tenancy agreement because the council may be under a repairing obligation in the agreement which you can enforce.
Regarding the mail, if other tenants/occupiers take your mail then they will be liable criminally for that. Not the council or freeholder.
Any questions or queries?
Happy to assist further.
The title documents do not help.
What you need is the lease to see who is responsible for repairing what. You can acquire a copy of the lease from the Land Registry.