OK, first, it is not true that folks on disability are getting a 19% cut.
What is true is that Medicare costs rose and those on SS are protected from the hike, while those not on SS are protected - the extra for them gets put on the other Medicare beneficiaries who are not collecting.
Also, if you are found disabled by the SSA, the only thing your SSD check will do is prevent you from the WELFARE program called SSI (Supplement Security Income) - but that only happens if your SSD is bigger, so your SSD is more, and therefore, usually preferable.
That all said, I think a 150 increase in an supplemental plan that may be being deducted from your SS check is a rather large increase (if it WERE that) since you say you didn't change anything. But that is where I'd start: I'd check to see what the carrier is charging to see if they increased their rates. Then I'd go to http://ssa.gov/myaccount
From there, create a passworded account and download your benefits statement that should show you what the gross check is and all deductions. You can compare this to what was deducted last year, to see what was changed.
It IS possible for the SSA to screw up and overcharge, so if it continues to NOT be clear or make sense, I'd take a trip down to the local SSA office.