Calli

Yes they do. The local agents are Herholdts who cover them and covered the Sunsynk batteries - Sun-batt, which was EEnovance branded as Sunsynk.
I'm sure there is a way to add in a third EEnovance. Herholdts would be the best to ask.

I am seeking some advice regarding my battery upgrade. I am planning to add a 5.32kW battery to my existing 5kW inverter, but I have been informed that Sunsynk has discontinued its batteries. As a result, I would need to purchase a 5.32kW Eenovance battery, which was originally the manufacturer behind Sunsynk batteries.

I understand that the Eenovance battery must be set as the master, while the existing Sunsynk (Sun-Batt) battery would function as the slave (see attached document). Additionally, firmware updates for the Eenovance battery would be managed via Wi-Fi, whereas the Sunsynk battery would require a manual PC connection for updates.

There are still some Sunsynk batteries available, but here’s the issue: they are approximately R8,000 more expensive than Eenovance batteries, plus an additional R3,600 installation fee. Given that Eenovance originally manufactured Sunsynk, is it really worth spending the extra R8,000 for a Sunsynk battery even though there might be a firmware update issue?

I was quoted the fee for installing an additional battery by the original installer and supplier, but on another forum, I was advised that the cost is too high. What would be a reasonable price?

I would greatly appreciate your opinion on whether Sunsynk or Eenovance would be the better long-term investment and an acceptable instalation fee for 1 battery.
Thank you.
EEnovance_Battery_Compatible_Declaration_250213_(5)_(1)[1].pdf

As per Sunsynk advice.
We moved the EMI filter from under the hob. Sunsynk specified that the filter is specked for the 5KW inverter and should be between the inverter and grid port, this then will not have any current draw through this filter to go to hob.
If not done, I would have to buy a 30+A filter if it remained under hob.
Thankfully, Hob now works well.

As per Sunsynk advice.
We moved the EMI filter from under the hob. Sunsynk specified that the filter is specked for the 5KW inverter and should be between the inverter and grid port, this then will not have any current draw through this filter to go to hob.
If not done, I would have to buy a 30+A filter if it remained under hob.
Thankfully, Hob now works well.

Some feedback.
The good news: the problem has been resolved.
Sunsynk gracefully supplied an EMI Filter (n/c) which was installed and now the Smeg Hob works.
Thanks to all for the discussion and advice.

Excellent explanation by Yellow Tapemeasure, thank you. 
Article had thrown a lot of clarity to my quest in understanding the intricacies. 
One of the suppliers I got quotes from, suggested I look at Luxpower 
LUXPOWER 5KW INVERTER 48V 80AX2 MPPT 120-450VDC/ WIFI / PARALLEL 
BL12048 1 SOLARWIZE LITHIUM WALL MOUNT 120Ah 48V 5,8KWh
What worries me though (not that it is cheaper by R16k) but that it does not have CT and 2x MPPTs. 
Yours thoughts would be greatly appreciated. 
Thanks