Call 121 and tell them to take the request, they will usually say okay but rarely take disconnection requests to process.
I was able to get it disconnected after 4-5 days, but it was a big circus.
I had to call them several times, they kept calling to keep the connection, several emails, scolding etc. Finally it happened, but it was quite a hassle.
One of their so called managers even asked me to check if my neighbor wanted the connection so that I can give it to neighbor instead of disconnection.