Is this Section 21 correct?

Our tenancy was meant to come to an end on 12 May 2019.
Our landlord via his agent sent an email asking if we wanted to extend. Prior to this our landlord has wanted to sell the property but is not getting any joy as the property is not in a good state. We confirmed we wanted to extend. We have several emails where they asked for the signed tenancy, which was eventually sent (hard copies). The landlord stays abroad do the agents sign in lieu of him.
We did not receive the signed copies back ( which is the norm - has happened previously).
On 13 May 2019 ( the date of the renewal) we received a section 21 notice to vacate.
We have tried explaining to the agents and landlord about the situation but they insist that there is no tenancy, nothing was signed and also actually said that their employees sent an email but that’s about it.
It seems like the landlord wants to renovate the property as it has a lot of issues and wants to sell.
I have to add our landlord has always behaved appalling in the past with regards to repairs and I don’t mean cosmetic - these are leakages, having no hot water in winter etc.
We wrote back questioning the validity of the section 21 and being given notice within the first two months of the renewal as the section 21 says this should be given before or on the day the tenancy ends (12 May 2019).
We are getting aggressive About about the landlord wanting possession.
We have said we will move but require time till 13 sep 2019 to do do as there are a few appointments and family obligations which are making it difficult apart from finding a place.
Please advice as I feel the landlord is taking advantage of our niceness.
We haven’t received the ‘unsigned’ tenancy back.