Vodacom unfair downward migration without consent

In May 2020 I signed up for a 10mbps upload and 10mbps download fibre line with Vodacom. I have recently started working from home and thus need to upload alot of big documents on a daily basis, to my surprise I realised I was only averaging on about a 1.5mbps upload speed, when I called in to enquire as to why, I was told that the ISP provider had changed in my area from DSV to Vumatel and because Vumatel is more expensive they decided to downgrade my package to a 2mpbs upload and a 10mbps download speed without my consent and thereby not complying to what I initially signed up for. They are now telling me if I wish to get the speed I originally signed up for I need to upgrade my package to a more expensive package. Please sort this issue out immediately before further action will be taken.