One party cannot unilaterally withdraw a contract after the other party has already accepted.
It is standard contract law in the US, Taiwan, and most other nations that an offer to enter into a contract may be withdrawn at any time before it has been accepted, unless the offer states that it will remain open for a certain period. But after one party makes an offer and the other party accepts, you have a contract and in general it may only be modified or terminated by mutual consent of both parties, unless the contract contains express language to the contrary.
You mentioned a verbal agreement in this case. I’m not sure what that means, as verbal can mean oral or written, but a contract may be either of those – oral or written – and both can be equally valid, binding and enforceable. The huge difference, of course, is that it is much easier to prove the existence and terms of a written contract. One can sue for breach of an oral contract, take it to trial, and if one has good witnesses or is more credible than the other party, a judge may find in your favor – deciding such oral contract existed and was breached by the other party, causing damages for which you should be compensated. But, as noted, it’s a lot easier to prove all that if the contract is in writing.
As for acceptance, the best way to prove that is by signing the written offer at commencement of the agreement, but that’s not the only way to accept an agreement. One can also accept orally (but you’ve got the same problem of proof) or by performance or reliance to your detriment.
Finally, when you say a contract’s not worth the paper it’s written on, that’s a completely unfair statement if you haven’t yet hired a lawyer and/or sued. A contract is just a binding agreement. They are broken all the time. The purpose of a contract is to give you the right to a legal remedy in the event it is breached. In other words, if you just bitch about it you haven’t availed yourself of your legal rights. If you want to enforce the contract, it’s necessary to threaten them with a legal action or actually file a legal action.
Of course, doing so is time consuming, expensive, a pain in the ass, and the results are not guaranteed, especially in Taiwan’s lame justice system. So, it’s only worthwhile pursuing a legal action if (a) you’ve got a very strong case and (b) your monetary damages are great and provable. If you’ve only been screwed out of a few thousand NT it’s clearly not worth the effort to hire an attorney and/or sue.
Angry people who feel they have had their legal rights violated often want to sue “out of principle,” to “teach them a lesson.” Any smart attorney will tell you, those are the cases/clients to be avoided, as no good will come out of them, the client will only be angry in the end, and he/she will blame the attorney.
One of the great lessons people should learn about the legal systems all over the world, is that often life sucks, often you will get screwed over, and often the best recourse is to recognize that “dammit, I got screwed by that evil bastard,” and to move on with one’s life rather than dwelling in the past and seeking revenge/retribution/remuneration.
Not saying that is or isn’t the case in your situation, but just something to think about. Good luck. 