I don't know that they ever flat-out phrased it as extremely as "impossible to get addicted to", but Purdue Pharma definitely made puffed-up claims that the extended-release nature of OxyContin drastically lowered addiction potential compared to immediate-release opioids. They were fined $600M for aggressively misleading marketing about its addiction potential and reduced side effects [1].

[1] https://www.nytimes.com/2007/05/10/business/11drug-web.html