Debit order not deducted as agreed with vodacom

I have been a loyal customer of vodacom for more than ten years. I have been paying my account very well until this month when Vodacom decided to deduct R150 of upgrade versus what was due on the account. Now I'm receiving calls as if this was my mistake. When I did an enquiry I was told I did not have money in my account when Vodacom wanted to deduct and I then requested Vodacom to prove that to me because it was my pay day there was no ways that they deducted their money.The second person I spoke with then told me no it was because of the upgrade. Now what I could not understand is do we amend debit on the exact date that your normal debit order supposed to go off? Just for R150? Versus amount Due

Today I received my statement and I can you now that I will not be able to pay such amount on April. I would like Vodacom to take ownership of their mistake and credit that amount so that I am able to pay the correct amount due for this month. I can not be help liable for their mistake.

I would also like to ask Vodacom to make sure that my credit score Or rating will not be affected by this. I will not have overdue on their account. They will have to update it as if they have received the money.

I would like to receive an updated statement for the correct amount to be deducted in my account end of April.

Alternatively Vodacom must prove to me that I had insufficient funds when they want to deduct the amount. I have asked twice the Team Leads/Credit manager to call me no one was available at the time I was willing to negotiate now with president announcement i will not be able to afford it.