Mdalisu not responding to email regarding a cancellation of services letter

I have sent this company a cancellation letter for the services of debt review status removal, and to not deduct anything from my account. They have not responded to me as to date. FNB said I can only cancel the debit check mandate with Mdalisu. I sent emails, what'sapp and even phoned them, but the phone was dropped to my face several times this morning.