Unauthorized debit order with no communication to your clients!!

I went to a Spec Savers in Greenstone Hill a month before immigrating and was told in store that I have an amount of R3849.00 available to use against my spectacles as in store credit. After leaving the country I noticed a debit order of R250 that went off my bank account at the end of July. With me being out of the country I could not phone anyone at Specsavers so I sent a WhatsApp to Fevertree as I noticed that's who debited my account. I was told by someone who did not give me his/her name that I need to pay the full amount and that somebody from Specsavers will be in contact with me via email. I have not heard anything yet but only received a settlement letter over whatsapp from this person. A few days went by and I sent another whatsapp to have the settlement emailed to me but was sent another person's account statement. After giving my ID 3 times over these whatsapp messages I was told that it is my responsibility to update my email address and that they still have an old one on record.

My question is, HOW ON EARTH can you debit an account without even speaking to your clients and making sure that there is such an authority given by them, how is Spec Savers doing your job for you and why do your clients get debited and have to resort to whatsapp messages like we are all stuck in highschool??