New management company appear out of thin air demanding thousands?

Hello, I bought a 999 year leasehold flat in January 2015. Despite thorough searches by my solicitors, no management company was identified and the local London council who was the original freeholder wrote a reply stating that they were not the freeholder.

Roll on to March 2023 and a Management Company that I have never heard of or dealt with has written asking for block management fees. We are a block of 6 flats and they are asking for ground rent and management fees for maintenance and insurance amounting to about £1800 per flat.

Since 2015 we have maintained and managed the block ourselves, taken out our own block insurance policy and carried out fire risk assessments and so on. This new management company is completely unknown to us, has written no letter of introduction and just sent us a straight bill.

On their invoice, it states it acts on behalf of the freeholder which is the London Borough which has written to me in 2015 denying they are the freeholder. So far none of us have paid but the pressure is mounting and we are not sure where we stand.

Any advice would be gratefully received,

Sageer