I am sorry to hear about the problems you are running into.
Do you mean that the SampleTank 4 ("ST4") plug-in does not appear is Pro Tools' list of available plug-ins? Or that one or more SampleTank instruments are not available in ST4's browser?
-----------------------
As this is primarily a user to user forum, someone-else may chime in [#]. Meanwhile, the best thing to do is
check the FAQs, via here. If they do not resolve the issue, there is a link to the Technical Support form, for some one to one investigation and help. Response time is usually within 2 working days (US (East Coast) Business hours, generally), but in the current circumstances please allow some more time.
[#] But please remember that the same symptoms do not necessarily mean the same problem.
And, to help others who run into a similar problem, please let us know what you did to resolve the problem.