See how your domain mytracer.mobi is resolving right now.
mytracer.mobi. 86400 IN NS ns.dns2.co.za.
mytracer.mobi. 86400 IN NS ns.dns1.co.za.
mytracer.mobi. 86400 IN NS ns.otherdns.com.
mytracer.mobi. 86400 IN NS ns.otherdns.net.
;; Received 138 bytes from 199.249.126.1#53(b2.mobi.afilias-nst.org) in 18 ms
mytracer.mobi. 7260 IN A 196.38.40.144
;; Received 47 bytes from 197.242.144.5#53(ns.dns2.co.za) in 272 ms
It is using the name servers as shown with NS records and still pointing to your old server IP 196.38.40.144.
So you will have to change/edit the A record with new server IP 154.0.160.35 from your name server end. Thant means A record should change where your name servers are pointing to.
I hope this will resolve your confusion.