Impossible to Cancel a Contract via Retentions E-mail

My Mother went over to the UK last year December (2019), she has since tried to cancel her Vodacom contract as she has decided to stay in the UK for an undetermined time; as such the Vodacom contract is of no use to her (and it's term is up). She is not able to contact the call centre and cannot send an sms query either since she is in London (this is a 3G contract). She has been e-mailing retentions since 29 March 2020 to no avail - no one answers her, no one confirms receipt, no one actions the request, ABSOLUTELY NOTHING HAPPENS! I have been copied in on all of the e-mails she has sent and she is now at her wits end and will be reversing the debit order as she has given 2 months notice and Vodacom hasn't actioned anything at all - pathetic service (or rather lack of service). What steps can be taken for someone to acknowledge and action her request (bearing in mind she cannot call in or sms - her only way of communication right now is per e-mail)?!? She has now sent 5 e-mails to the following e-mail as noted on your contacts list - ***. The number in question is ***.