Staff insisting on 3 months bank statements for debit order change, very suspicious

I sent in my proof of bank account to change my debit order. Many emails later my debit order is still not changed and the staff are acting suspicious. After sending the proof of bank account and completing a bank details change form, they now request that I send three months bank statements? I advised that I will not send it as they have enough legal documents and confirmation of my bank accounts. Today I got a call from Thabiso in the retention department this morning asking for my 3 months bank statements again. I advised that I will not send it, I will rather EFT every month. This is very suspicious and I am not comfortable at all with the emails and call received this morning.