What you have said sounds really ridiculous.
You blood group
DEFINITELY cannot change.
It has to be either O positive or O negative.
One possibility that comes to mind is that you might have a rare blood group like the Bombay blood group, but even that would show up as O negative on testing.
You need to go to a tertiary institute, present them with all the documented reports of your past blood group typing, and then ask for a final opinion on paper.
Definitely, one or more laboratories has messed up with your reports, and that is criminal.