Unapproved increase in debit order

Had a R59pm contract (done telephonically, confirmed that capped at R59pm/500mb). Come November, December and January 2021 an amount of R454pm was deducted (all previous deductions were R59pm). Emailed the complaint, referred them to the recording, they declined the refund. Clearly breached their own contract and is now hiding behind the "system". It would appear as if they have summarily changed the terms and conditions by themselves without my consent. Stay away from Yellodata.