Very poor service

I have been a Vodacom client since 1998. For several months I have been trying to resolve an upgrade problem with Vodacom. I have made at least five attempts to resolve this. The problem is that I last upgraded in August 2018, but the system indicates that I am only eligible for an upgrade in November 2021, which makes no sense as I have a 24 month contract. Every Vodacom customer service agent I have spoken to (I think I have spoken to around 8 different people) has indicated that the dates on the system are incorrect, but that this issue needs to be resolved by a 'Solutions Expert'. On all occasions I have subsequently received a notification that the call has been closed (without explanation), but the issue is not been resolved. All-in-all the level of service has been very poor. My last reference number was ***.