I don't think we can be anymore
help.
If I can summarise and you correct me if I'm wrong.
1) You've previously had your phone connected via BT in your car and were able to see and control it in the MFD settings on your dashboard?
2) It's suddenly stopped appearing in the MFD but your phone is still connecting to something?
3) You can't see anything to do with BT on the head unit's display or in the menu?
4) You've reset the MFD settings using the steering wheel controls to factory and that's not worked or done anything in regards to the BT?
The only thing left is to know what head unit you currently have in your car. You have to take a picture of it or find out what it is and tell us so we can try and assist you more.
We don't know anything about your car or specification.
5) Did you buy it brand new?
6) Did it come with factory fitted SEAT BT already installed?
7) If you purchased it second hand, do you know if the the previous owner installed a third party BT unit to it? i.e, something from Halfords or another type that has nothing to do with SEAT or OEM.
We now need you to give us information on that head unit so we can try and eliminate options. For all we know, you could have, for example, a Parrot BT installed which means we're all wasting time trying to figure out a wrong solution to your issue.
Do you have a microphone anywhere that you can see? By the rear-view mirror or sun-visor? Or anything by the heater vents?