I've had a Tado for nearly 3 years. Can anyone tell me when the app became free?

Hi, This is my first question/comment so please go easy on me!

I had a Tado fitted by Homeserve in December 2016 and was told there was a charge for using the app. I paid £3.50 am month for the first year then it went up to £7.

I was looking at changing to a Hive as their app is free and then I discovered the Tado app is now free. I have no idea what I'm paying for (we only have the basic combo boiler set up and thermostat)? I have a feeling I'm being ripped off 😤

We pay to Homeserve and they can't tell us what we're paying for and don't seem to have a record of it but it's them we pay to!!