Billed for a device I didn't take at the store

From 2015 trying to get someone to assist at Telkom in Johannesburg. I was assisted by Marcus and he was offering me a phone I didn't want, when I saw that I told him I'm not interested and I won't be taking the phone .He continued with the application and I get statement that I should pay. I'm now listed as a bad payer and when I go Telling no one can assist me. They can't even look at the records. Pleaase help as this pops up whenever I'm trying to apply for credit