cancellation letter request (unhappy)

I registered with this company since 2018, they promised to pay my debt ,but they did not ,now I cannot even get out from debt review from them I have been requesting cancellation letters ,but I’m not winning,I changed my banking details in order to stop them from deducting money since they were not paying anyway,if it wasn’t for them ,my debt would have prescribed,I do not advise anyone to sign up with this company,I jst want a cancellation letter so I can work on my credit