Nedbank home loan not moving

I registered a bond with Nedbank on 2000. On 2009 I had the balance of R120000, they offered me a loan of R280000 on top of the balance. The amount of balance then changed to R589000 on 2009. The bond was registered to carry on for 20 years, now since 2009 to 2019 its been 10 years and I've been paying every month but this bond is not moving, after 10 years the bond is still on R447000 from R589000 on 2009. It's like for this 10 years I only paid R142000, but I have been paying R5700 every month. Why the balance is not half of the amount because it's a 20years bond and I have reached 10years already.