As you have a share in the freehold then you are a freeholder, the freehold will be jointly shared amongst all of you. You need to know some basics ie did the directors employ a management company or is the development self-managed. Find out who the directors are, this will be on your documentation. There will be a chairperson, secretary and treasurer at the very least. I would expect that there will also be a number of directors.
Go onto the companies house website and look up the name of the mangement company, there will be a company address and a list of involved people. You could write to each of those people at the company address. Be formal, state facts, don`t say please or be friendly, just straightforward facts with dates
Date everything and keep a record and file of written letters. Sending letters via recorded delivery is far the best way, take a copy and file it with the date received at destination
The leasehold advisory service is helpful but be sure to know and understand the basic facts concerning your freehold and management company