Telkom cellphone contract double deducted

I have a cellphone contract with telkom of a Samsung A21s which they deduct R259 monthly , on the 31st of may 2021 they deducted R518 and after calling them they told me they didn't deduct in April and for that I should find out with my bank, but my FNB bank statement shows they deducted their R259 in april 30th, I don't know how their systems work but we are not safe with our money I want to pay them manually.