There’s no reason to blame your lack of understanding what a mirror does and what a testserver is on CCP.
But let me elaborate: A so-called mirror is nothing other than a copy of the tq database, migrated to the sisi database. Which means it will also (correctly) copy your current clone state.
Let’s say you have 30 days of subscription left when the mirror happens, then sisi will get the information that your clone state is omega and will be for another 30 days. If you buy more omega time after the mirror happened, this information will be stored in the tq database, but will not go into the sisi database. Which means after 30 days your account will become alpha on singularity, even if you’re omega on tq for longer.
And for the “worthless” message from CCP: It was always clearly stated that there is no ticket support for the TESTSERVER, which is provided As is, so why would one be surprised for not getting any support?