My husband's T4 includes contribution for CPP2 , but the CPP earnings reflects YMPE, not YAMPE. CPP2 contribution reflect as overpayment, and refunds. How do I fix?

[ctlyf]

I've connected with his employer, and she will not change the T4, based on instructions from CRA and within her software that Box 26 is earnings base for contributions in box 16, not box 16a. Conversely, my employer included YAMPE in box 26, reflecting the earnings base for both box 16 and 16a. If I change box 26 to reflect YAMPE, I'm concerned CRA will just adjust based on T4 that was filed. I also don't seem to have any option to adjust earnings in Schedule 8.