Double-charging of cancellation fee

I recently requested an early cancellation of a data / tablet contract, and was quoted a cancellation fee of R115. This fee had to be paid to Vodacom, and proof of payment was to be submitted with my cancellation request documents for processing. The contract was duly cancelled as instructed, but when I received my final statement I saw that the cancellation fee had been invoiced, but my payment did not reflect. The R115 was therefore included in my final debit order (i.e. it was paid twice). However, despite numerous e-mails to Vodacom's cancellation department to get this matter resolved, I had received absolutely no response other than 'read receipts' until the case was summarily closed. I requested a re-opening of this case, but still no response. As I sit here, Vodacom owes me R115 that it has incorrectly been paid twice, and it looks like they are assuming that if they ignore me long enough, I'll go away. Not going to happen! On the contrary, the PR damage that their failure to respond will ultimately cost them more than the R115 that they owe me. Thankfully, as I have emigrated, I never have to deal with this monolithic organisation again, but I will not rest until I receive a proper response and the refund of the amount double-paid.