It’s not WiFi it’s broadband, WiFi is how you connect can connect some devices like iPads , iPhones etc to your router ( your broadband router ).
Yes you can have broadband without phone or TV , the price for broadband only is obtained simply by removing the cost of the services you want removed from the bill , as you don’t say what you currently pay it impossible to say what you would ‘save’ but you can easily find out , just look at your bill , and remove the cost of what you pay for your phone service and tv service…in my case , I have telephony that costs £3 a month , I’d obviously save £3 a month if I removed it .
You need to take into account if you are inside any minimum terms ( in contract ) getting rid of some services while inside the minimum term attracts early termination charges , and if you get a discount for having a bundle of services, that discount may disappear if you don’t keep the bundle of services.
Most BT contract are 24months , 12 month ones are available but cost more per month .
Yes you can alter your package over the phone with the caveats about minimum terms and potential discounts
