You may feel you need to pay under protest and later try to reclaim for overpayments (or challenge it in general) via a formal process. This is a personal decision. If so, may wish to take legal advice, or consider the guidance and template language from Leasehold Advice (noting the FEC is not a service charge). If so here is a template try this template to get you started.
We continue to work with R&R on the invoicing and calculation issues.