With regard to the emails, he is clearly harassing you. That is a police matter and you can get that stopped by the police under the provisions of the Protection from Harassment Act.
If you think the work is excessive, or the cost is excessive, or you think that the work is not required, and he is insisting on it, you can simply tell him that and if he decides to pursue you for the money, you can refer the matter to the Leasehold Valuation Tribunal.
The notice may be invalid and if you raise the issue all he will do is give you another one.
The local authority must offer the freehold to all the tenants and you should have been advised. If the landlord sells without providing the Right of First Refusal, the tenants can serve a notice on the new owner demanding details of the transaction, including the price paid; they can then take action to force the new owner to sell to them at the price he paid. In your particular case that means that the freehold would be owned jointly with you and the landlord.
With the landlord not replying to enquiries, unfortunately, there is nothing you can do about that unless there is a provision in the lease which compels him to do so and if there is that provision, there would normally be fee of perhaps £150 for doing so.
Situation with landlords not replying to enquiries is not that uncommon to be honest.
I see that you have asked for a telephone call. I can submit this to you as a premium service which there is an extra cost. You can take the offer up or leave it in abeyance.