Extra charges on account (Roaming)

I've had a R39.25/month contract for nearly 2 years and all of a sudden it jumped to R109.28 and when I called to ask what the extra charge was for, they said I incurred roaming charges. First of all, roaming on my phone is switched off as I never intended to use roaming at all. I asked who activated the roaming on my account they said I did (which I did not), well ever since it was activated I never used it once and was quite surprised when my invoice came to me. I asked for evidence that it was me who asked for it to be activated and all of a sudden the system couldn't load these details. He was fine to get all my details and to see what the extra charge was for. Apparently it was activated in August 2017, which I never asked them to do.