Since I am replying on the go, the response (as well as my last comment) may be too brief and not cover all aspects in full.
Analytically considered, it is simple. Pacta sunt servanda, contracts must be honored.
Are there exceptions/laws that allow one contracting party to unilaterally exit the contract contrary to the contractual agreement?
Yes, there are, but they do not apply given the information provided.
Are there important pieces of information that might cause a bank to react contrary to usual behavior?
Yes, there were, but they were only disclosed little by little.
Bankers (still mostly merchants) do not like it when information is withheld, neither positive nor negative. Complete information can lead to a different outcome.
At the outset, there was the question of whether it is professionally correct. And the answer is: Yes, it is professionally correct. So why should something be done differently?
At the moment, I only see someone trying to enforce their supposed own gain (it would first have to be checked whether this is really the case) at the expense of the bank (administrative costs, additional effort) without having a basis for this.
And the decisive answer: No, the bank is not obliged and is in the right.
The collateral is indeed higher than necessary, but there are two important components that bind you.
1) You probably have interest conditions based on a real estate security. Perhaps even a Pfandbriefbank, which even refinances itself this way. So the collateral house is essential solely for the conditions.
2) Repayment agreement through the accumulation of a life insurance policy. So this cannot be dissolved either.
The only thing, besides stopping the premium payment, that could still succeed would be the cancellation of a life insurance policy without repaying the loan, as long as sufficient guaranteed capital remains in the second life insurance policy.
But even here applies: The bank is not obliged, pacta sunt servanda. Etc...