Contract Cancellation nightmare

I am trying to cancel my contract that ends next month. I went to the store, they said I need to wait till October. I phoned the number they gave me 1st Oct 2019 (+***8), but there is no option for cancellation. I did an online request that they need to phone or contact me. Got an email reply asking for details that I gave. Still no response and this is the 3rd day. I emailed retentions with a cancellation letter, just for them to reply that someone will contact me within 24-48 hrs, still nothing. My email query nr is [#964038], with every response they ask the same info??!! Past pathetic!! I have been paying for the last three years on time every month and they can't even deliver the most basic customer service.