Digital care is robbing me

I took a phone lease in April 2023 for 12 months. Total repayment was R3770. I paid this in full longer than 12 months because I missed 3 months payment. This company then has debt collecting companies call and email me. I send the company proof of payments (bank statments) the lease agreement which proves I have paid them back in full. They persist I am still in debt with them for R2000 + areas. They say it was a 24 month lease. How does one pay R3770 in 24 months when the no th repayment amount is R249.99? How have I paid for 15 months but still owe R2000 + arreas? This have effected my credit score. I called them multiple times, they are *****ulent because their name changed from digital care to boltech. Their customer service is lazy, the managers never call back. I have explained and sent proof over and over again and every month they say I owe more. This is effecting not only my credit score but, my mental health. Make it stop! I do not recommend anyone use their service and clearly I am not the only person they do this to!