Q&A

 Master

From what you've written, I think it's possible you have damaged the master cylinder or the ABS system if so equipped. When pushing the pistons back into the calipers, it's important to open the bleeder valves and allow the used fluid to drain into a container rather than push it back up through the master cylinder into the reservoir. This way you avoid getting moisture and grit from the calipers into the very sensitive ABS valves and master cylinder.
Without ABS, probably your master cylinder is contaminated.
With ABS, you may have air in the ABS unit or it may also be contaminated.
If you get a new master cylinder, bleed it on the bench first to be sure there isn't air in it, then install it and bleed the lines at the ABS unit, then at the wheels. I hope that the ABS unit avoided damage.
Good Luck.