Sim upgrade to lease solar panels

We have owned our property for 8 years and it was 12 years until a leased solar panel agreement - we don't pay anything but we don't get full access to the energy our solar panel provides. It was a nightmare at purchase to find out who 'owns' the solar panels to get out purchase agreed but since then all has been fine until this year - when we have received numerous correspondence from renewable energy solutions services - to arrange to update our SIM with the changes in the 2g/3g network. We have replied by email or telephone call to every communication in May we received one stating legal action if we do not respond in 10 days - we did ... we still have not heard anything. I've sent a follow up email this week still nothing. Has anyone any advise on how to actually get this company to complete the update? TIA - as panicking as we have just gone down the route of an electric vehicle and having batteries installed!