Edgars want me to pay for insurance services I dint receive please help

I have problem with Edgars, i sent my phone for repairs that was still under warranty in August 2018 in Midrand boulders Edgars which was later closed when i called edgars head office they could acknowledge that i have sent my phone to the store but they can't seem to find it. The store manager called me saying they will give me a voucher equalling my phone value but they are un willing to write off the unpaid insurance on the phone, i stopped paying insurance since edgars was refusing to return my phone. I told them i wont be paying for services i didn't receive. Edgars decided to close to query without resolving it i now keep on receiving calls from edgars debt collectors sayinh i owe edgars. I regret the day i bought my phone from edgars since they are now affecting my credit record for something i didnt do.