If you have done serial test from different places and it still dsame then your mother have some explanation.
Biologically, AA AA = AA. Your mother gives one letter, your father gives one letter. If they are both AA, they only have A to give.
So if you're AS, it’s either the lab that did the test for your parents made a very big mistake (which happens), OR the lab that did your test also made a big mistake.
Take your parents to a highly reputable lab and retest everybody first. Specifically ask for an HPLC test or a DNA genotype test. They are far more accurate.