Gareth Edwards has an excellent piece on the phenomenon of the "trust thermocline". I mention this because I've been a (mostly happy) TPG customer since 2008, but have just migrated my NBN connection, static IP address, and 4 x SIMs to another ISP. TPG has crossed my "trust thermocline".
In most cases, though, the only real solution is to avoid crossing the trust thermocline at all. It requires placing emotional engagement and trust at the heart of product strategy, and accepting that the causes of trust failures are non-linear. Businesses need to address their customers’ complaints early and not dilute the value of their product. Informing users that prices are being increased because new features are available can damage trust if those features weren’t asked for to begin with. Just because a consumer swallows a new charge or price increase doesn’t mean they accept it as necessary.
TPG has offered pretty variable customer support, but - unlike Telstra and Optus - remained contactable during COVID. There was a weird time when I was the only one of my friends who could actually get support from a human being from their ISP, because I was with TPG.
However, my recent interactions with TPG have destroyed any trust and goodwill they built during that time.
- Lying to me in an effort to get me to purchase a new mobile device. I've received many emails from TPG claiming that w.r.t. the 3G shutdown "We [TPG] believe your mobile service may be impacted due to your location and the device you use, so it’s time to start thinking about upgrading to a VoLTE compatible 4G or 5G device as soon as possible to avoid any interruptions to your service.". When I called, concerned, I was told that this email is sent to all customers regardless of their device or location. It's just a sales scam.
- Continuing to send these marketing emails, and SMSs, despite me opting out in three different ways: by Web, by SMS, and by calling (several times).
- When I logged in to check what was going on, I saw that TPG plans to stop providing email, and is encouraging customers to migrate to an email provider who won't even provide pricing information on their service (and who has a shockingly lax privacy policy).
I've filed a complaint with CAV and the TIO over (1), and ACMA over (2). (3) doesn't effect me directly because I'm a (happy, paying) Fastmail customer, but it eroded the last dregs of trust and goodwill I had for TPG.
Losing one customer, even a customer who's been on the books for 15 years, doesn't exactly constitute a crisis 
But I wanted to post this feedback on the off chance that anyone from TPG cares & is reading the forum, and to encourage people to look elsewhere. I was positively surprised when I did, both by the deals on offer, and (in the case of the provider I chose) a prompt callback from a local call centre.
Oh, hey - somebody from TPG called me back! ... unlike this weekend when I was told I'd receive a callback, but no-one called. I guess complaining in public gets results.
The supervisor took the details of the emails and SMSs I'd received after opting out, but then decided to start arguing with me that the phrase "your mobile service may be impacted due to your location and the device you use" was technically true, because it may be the case - they just didn't know, so sent the marketing email to all customers just in case 
Not "we're sorry you were needlessly troubled" or "we understand that less technically savvy customers might have bought a device they didn't need" - just arguing on a technicality.
Anyhow, once she learned I'd already raised a complaint with CAV, the issue was escalated, and the call ended politely.
But if I had any doubts about my decision to switch away from TPG, they were utterly dispelled by your supervisor trying to explain how your statement may have been true. Just shocking.