Horrible Customer Support, page-41

For some actual data about TIO complaints, the report was released a few days ago for last year, if you look over a few years all telcos have improved, but these numbers dont take into account that number of customers have changed over that time.
Complaints per service is the data we really need to compare properly, but its not possible to breakdown properly as only count complaints per customer, and different types of services attract different levels of complaints, eg mobile vs fixed, SMB vs consumer.

Telstra, TPG and Optus have seen the worst improvements.

		2016-17	2017-18	2018-19	2019-20	Change 2016/17 to 19/20
1	Telstra	76650	82528	66402	66612	-13.10%
2	Optus	30120	40665	31629	26205	-13.00%
3	TPG	6995	6248	5380	6471	-7.49%
4	Vodafone	10684	9752	6784	6412	-39.99%
5	iiNet	10170	7719	5663	5723	-43.73%
6	Dodo	3309	3120	1863	1573	-52.46%
7	Southern	2068	1484	1366	1300	-37.14%
8	M2 Commander	1704	1565	1096	1160	-31.92%
9	MyRepublic	1816	1816	1286	769	-57.65%

Latest report here
https://www.tio.com.au/reports-updates/annual-report-201920