Ground rent issue/dispute

Has anyone had or having a similar scenario with ground rent collectors; my current dilemma: 

I have an issue with an Agent collecting ground rent for a flat I rent in Northampton; Homeground. I was paying ground rent from Jan – Dec of £250 per annum to an agent at the time called Chamonix Estates. The collection of the ground changed hands to another Agent called Homeground, which must have been in the year 2011 as I received from Homeground a request for payment of ground rent from September 2011 to March 2012 of £125.00.

I wrote to them stating I have already paid my ground rent in full for the year 2011, if they are requesting payment from midyear then I will require a refund of money I have paid for September up to December 2011. Homeground have not called to resolve this but instead keep sending invoices for payment of ground rent for their specified months saying it is in the lease documents, the previous agents did not bring this to my attention.

For the subsequent years 2012, 2013, 2014 I have been the paying the ground as from Jan to Dec of £250 as they have not given me a refund for the months already paid to bring me in line with the months they wish to collect from. I even wrote to the landlords to no avail. I sent in my previous invoices showing my account that I was not owing anything, but they have been unhelpful and have not clarified anything to me. The online system does not make sense to me regards the account. I will not pay ground rent twice for months I have already paid for.

Homeground have now sent in a letter saying I am in arrears of £123.36 inclusive of a late payment fee £45. I do not owe them anything. And I refuse to pay this amount. They say they are now taking legal proceedings if not paid. If the previous agents were not accounting properly that is not my issue and I have sent in my invoices showing my account in the black not red.

Can anyone advise or suggest anything?

Thank you in advance 😀

Jo