As an author should you stand up to the publisher who has breached your contracts, or Should you just bury your head in the sand and wait out the length of the contract to get your rights back? Multiple breaches are of an incurable nature.
Certainly, a complaining letter is in order. Multiple breaches and a refusal to remedy them in a timely fashion indicates 'bad faith', which means entering into a contract with no intention of honoring the terms. This is grounds for punitive damages and even lawyer fees. But it's risky, difficult to prosecute, and very expensive.
To put it in perspective, our lawsuit against an insurance company for breach of contract, where the evidence was clear and uncomplicated and the company's actions definitely in bad faith, took four years and $22,000 to fight. We won in settlement eventually, which meant that we only got part of what we were owed. But by then, we were exhausted and alarmed at the vast cost of the lawsuit. If it had gone to court, it would have cost much more.
The legal system lets people like you and I use it, but it's really meant for large companies to fight one another and to squeeze little people like you and I.
On the other hand, you can do a lot with formal letters and phone calls, and it doesn't cost much to get a lawyer to send an appropriate letter on legal stationery, even if you have no intention of actually suing.