messing my credit score

I bought a contract phone on 24 months instalments in 2023 April.The contract ended on April 2025.I fully paid the phone as per agreement.In march 2025 i made two payments in a week,I made one payment in their store , lucky for me i took a picture of the slip.For some reason, the payment i made in the store, was not captured or updated on the system.I called them and informed them, they requested proof of payment i emailed them,This is pathetic ,clearly their system is not trustworthy.All of a sudden my account is handed over for collections, i called vodacom again to inform them to allocate the payment, they asked for proof of payment again and reassured me that it will be updated.Two weeks later i still receive harassing calls from debt collectors.This stressful because it is messing up my credit score.Please update my payment or invest in a better system that will be smart enough to update payments.Your employees are acknowledging the mistake however no one is doing anything about that why your debt collectors won't stop harassing me while my credit score is suffering.