What would you do if your boss cut your hours from 56 hours a week to 29 hours a week even if he or she said they won’t cut your hours?

It all depends on the business and customers.

I'd ask why, and how long this was likely to last.

Work the 29 hours and look for a part time job on the side (or even a full time job). This may be temporary, due to covid, but if you can't survive on the pay from just 29 hours a week then you'd better do something.

During the business climate with COVID, I tend to think that this move is most likely due to the slowness of business in general and that he is struggling to keep the business going. What I would do if I were you, would be to ask your boss the reason.

Business conditions change and they have that right, just as you have the right to seek employment elsewhere.

I'd do nothing.  The boss is trying to keep the business floating in these hard times and doing what it takes to stay in business. 

I'd do something really radical. Say "Why did you cut my hours"?

i would be thankful i still have a job and find something else to do with my time then worry about that job

I would read my signed written contract to see how many hours I have been legally contracted to do, that would mean regardless of the actual hours worked, they legally have to pay me for the contracted hours........ if you do not have a written contract then you are on a zero hours contract, so legally the employer can give you hours or not and there is nothing you can do............. if that is the case I would look for another job and get a legal contract stating hours

Unless it is written down unfortunately there is no proof she  or he  said that. In this case it is your word versus hers or his i totally believe you. My answer is referring to the fact she or he  can lie and say she  or he never said that. Talking to her  or him may or may not work. You don't want to get yourself fired either though. In this case it is best left alone. If able it would be best to find another job  depending if your financial status  is good or not. If so I would let it go. If not and if possible my suggestion is to find a new job.

I am sorry this happend to you and I wish you the best of luck.