You are going to have a strange conversation, presumably something along the lines of , them , ‘ Hello BT’, you say, ‘I want to move to ‘Vodafone/Sky/Shell’, BT say ‘Sorry to hear that, bye then’, you say ‘They say they don’t serve my address’ , BT say ‘how is that our problem ?’, you say ‘I insist you sort this out’, they say ‘ You need to take it up with the company you want to use, Goodbye’.
FWIW, most of the providers you have quoted don’t chose to offer service over Openreach FTTP, that’s not BT blocking them, that’s just their own commercial decision , and as already said, VF are a complicated choice because they have their own FTTP network in certain areas.
The only way your inability to move provider would be if your address was incorrect on OR database compared to what’s on the Royal Mail/Post Office, in which case your OR address would need to be amended to match the RM/PO record, is there any reason to think your address is wrong on OR ?
