Sanderberry

Hi I’ve read through and can’t find anyone on my circumstances so am asking more questions about Coppen Estates. My house has a 60 year lease. I’d like to extend or buy the freehold version. I also have never received an invoice for ground rent so just want to get square with them. I understand it’s going to be difficult given the thread here but I’m looking for advice on potential costs and the process please. Thanks