To start with, think the switch off date was given before 2019, but Colvid was blamed for not changing the teleswitches in time, so it was delayed, and it has now had the cut-off date changed many times. They started in 1984, although considered back in 1964, and stopped installing them in 2014 the problem is internet does not keep up with changes, so a Google hunt can still find
If your electricity meter relies on the Radio Teleswitch Service (RTS), it will no longer function after March 31, 2024.
there has been huge numbers quoted as to how many teleswitches need replacing, but unlike the smart meter it was a one way communication, and there are a lot with simple time switches, so it seems the energy companies don't talk to meter readers, as that work has been outsourced, which made sense as all meters in an area read by the same team did not matter who you got your power from. But as a result it seems they have no real idea who has teleswitches fitted.
We have seen a report on this forum where a smart meter and teleswitch was fitted to the same supply. So can't even assume if a smart meter is fitted, there is no teleswitch.
The main problem is they have been unable to design an advert to tell people what the different devices do, miss information is starting with the government's own adverts, and the whole idea of off-peak supplies etc, is not helped when the tariffs alter area to area, as well as supplier to supplier, and the likes of Money Supermarket don't help, as it misses out some details.
I do have a way to work out what I have used, so I do stand a chance of working out what is my best option, but if I look at my British Gas app today it just says "Inactive accounts" lucky I took some screenshots, but in the main to look back on what I have used, I use the solar software.
For me, there is no problem, I can see without any shadow of doubt, I am gaining with an off-peak tariff. But for those who are still on a teleswitch, to work out the best option will not be easy. In 2019 we moved here, the electric supplier went to the wall, and we moved to British Gas by default. We like I am sure everyone else, worried about fuel prices, and the rates went up and then down so looking back to what we did pay, was the £140 per month due to high prices, or we were using a lot, or simply the energy company had not worked out a monthly payment which reflected 1/12th of the annual payment?
When we moved to a Smart meter, the bills did not really tie up with the change, so at no point was there a baseline to work things out from. We always had some estimation on the bill, as the bill would be to say the 20th April, but the meter read on 1st April, so we could not say how much it was really costing.
Even today I know last week used 43.21 kWh, and it costed £8.65 a nice graph

so minus standing charge 66.11p per day, means average price 10p/kWh so clearly I am better off with a split tariff, but with storage heaters it needs to be worked out over the year not per week and once you opt for a split tariff your often stuck for the year. How anyone can really work out if worth a split tariff with storage heaters I don't know?