Reclaiming property management service charges (FirstPort)

Planeteer

I bought a freehold property (May, 2011) on a street with leasehold properties that have FirstPort as the 'property manager. My transfer document states that for some of the exterior shared grounds, I am due grounds maintenance services, for which I pay £90 pm. However, each time I have spotted a gardener, they have counted the provision of services either by assumption of exclusion (due to my freehold) or even apparently by instruction. Only the latest property manager by FirstPort seems a bit more dedicated and has been in touch with the gardening service I (should) have been entitled to. 

I am wondering now what case or process I have for reclaiming the 10+ years of property management services I paid for but didn't receive? Should I go directly, or through a legal insurance?

Thanks for any advice.