During the current Coronavirus restrictions your supplier should not disconnect you. Get immediate advice if your supplier has said they are going to do this.
Even when restrictions are not in place it is still rare for your supplier to disconnect your supply, they will look to come to a payment arrangement or to avoid disconnection ask you to allow for for a pre-payment to be installed.
Although it is rare for disconnection to happen, it remains an option for your supplier if you cannot come to a suitable arrangement to deal with debt owed to them. Seeking advice as early as possible when you first fall behind with payments can help avoid the situation reaching this point.
Citizens Advice have a guide on vulnerable individuals who should not be disconnected and also the legal process your supplier requires to follow if they intend to disconnect your supply: If you’ve been told your energy supply will be disconnected - Citizens Advice Scotland