Vodacom Charges R17000 for Mistake They Made

Vodacom messed up my phone contract by upgrading my router line instead of issuing a new contract. I was told to cancel the upgrade and I would receive a refund and I could start the process again. It took them 6 months to collect the phone (which remained unused in its box). Once the phone was collected I was told I would receive a refund. No refund was received. Instead I received a bill for R17000 to pay out the contract (despite them having the phone back). I requested recordings of conversations numerous times and to date I have received nothing. I am a single mother and high school teacher. I cannot afford the time and money on this anymore. I am immigrating in 3 months and am now at risk of being blacklisted.