Looks more like you set up 3 routers and renamed each access point.
Lmao.
Id love to know how you apparently set up 3 different ISPs on the one phone line that goes to houses.
Edit:
You asked how you can't have 3 at once, Your house/apartment/whatever has a single(sometimes double if the place is divided up into two separate houses e.g. main house and then granny flat)
When you get an internet connection set up the ISP uses that line, no other isp can while its in use.
That is the same reason as to why when you change isp you have to cancel the current one before they can connect you.