FNB Connect wont give me an invoice?!

I ported my number to FNB Connect in 2017. I am now permitted to claim back my cellphone contract payment from my employer, provided I provide them with a tax invoice.

In January 2019 I enquired if I could add a device to my existing number but was told this is not possible. I was however told that I would have to take the device, including a second sim and a Top up L contract and that this would be on a separate invoice from my existing number. My employer luckily agreed to allowing me to claim back with the two invoices.

Now I have been told that I cannot be provided with an invoice at all because it is a device that happens to include a contract and I must check my bank account for proof. They deduct a monthly amount, it is a device including a monthly contract and now you wont give a monthly invoice?! UTTER NONSENSE. If this is the case the contract must be cancelled and I will give the device back because without this invoice my employer cant reimburse me and I cannot afford it! SHOCKING SERVICE!