two things, if the water is cold, anything cooler than about 70F, you need to be doing cold water treatments, this mostly removes the sucker punch effect when your face gets hit with the cold water. Super simple, mask off, face in water, inhale through reg or snorkel, exhale through nose until you are comfortable.
If that above exercise is the problem you really need to start doing exhalation drills in the pool until you are comfortable breathing with the mask off of your face, these are all lead up drills to an efficient mask clear. This is as simple as hanging on the side of the pool and exhaling as slowly as possible through your nose. Get to the point where you can start and stop the flow of bubbles. Once you are comfortable with stopping and starting the flow on one breath, add a snorkel so you can start breathing, but always exhaling through your nose. Once that is comfortable, alternate between exhaling through the snorkel and exhaling through your nose so you are comfortable mouth breathing without the mask on your face. At that point, go to the shallow end of the pool, and with a weight belt/diving brick, sit on the bottom of the pool and practice mask drills.
No offense to you, but if you are not comfortable with the above drills, you are not a safe diver, and really need to get that fixed. Having to thumb dives because of mask clears is just not acceptable and it is your instructors fault for passing you through. While you may be physically capable of clearing your mask, it is clearly a major safety issue for you. The above drills should be able to remedy this in a few hours btw, don't need an instructor, don't even need a buddy *just make sure you aren't hyperventilating so the lifeguards don't have to go acquire you*. If you are holding onto the wall and your feet are floating back, tuck your knees in like you are sitting in a chair and you will get sucked to the wall while you are doing these drills.
