There are two separate regulations that apply here...it is good to understand them both
The first is the reg that applies to obliserve. You can see it hereMILPERSMAN 1306-604
If you look at MILPERSMAN 1306-604, you see that obliserve is required if you attend a formal school (A or C) but that
If the members current service is sufficient to cover the obliserve requirement? Then there is no obliserve requirement. In other words, if you started school with 4 years on the contract, and the obliserve requirement for the school was 3 years? Then you would not have to serve any additional time.
On the other hand, if you had 4 years of service left and the obliserve was 6 years? Then you would owe two.
Take a look at the chart in para 3b
If your school was 31-38 weeks (and what you describe it was 9 months or 36 weeks) then your period owed would only be 42 months.
So I think there may be some confusion on the basic obliserve terms. If that is the case? I would point this out through your chain of command to adjust your EAS properly.
HOWEVER, if you stated in the NUC field, AEF and ATF you have to look at a separate reference
it is MILPERSMAN 1510-030
If this was you? Then you have to look at the table in para 10 to see what your obligations are.
Let me know if you have more questions...happy to help if I can