Tell that to the CDC.
Q: Can people who recover from COVID-19 be re-infected with SARS-CoV-2?
A: The immune response, including duration of immunity, to SARS-CoV-2 infection is not yet understood. Patients with MERS-CoV are unlikely to be re-infected shortly after they recover, but it is not yet known whether similar immune protection will be observed for patients with COVID-19.
Most coronaviruses do not result in lifetime immunity:
From the immune system’s perspective, some pathogens are unforgettable. One brush with the viruses that cause chickenpox or polio, for instance, is usually enough to protect a person for life. Other microbes, however, leave less of an impression, and researchers still aren’t entirely sure why. This applies to the four coronaviruses known to cause a subset of common cold cases, says Rachel Graham, an epidemiologist and coronavirus expert at the University of North Carolina at Chapel Hill. Immunity against these viruses seems to wane in a matter of months or a couple of years, which is why people get colds so frequently.
It's far from certain--at least based on the information known to date--to conclude that one COVID-19 infection results in long-term or permanent immunity.