Is it obligatory to only follow the fatwas of the Shafi'i school regarding the non-occurrence of divorce, and is it permissible not to follow the fatwas concerning the non-occurrence of divorce from a single school or a single scholar?

There is no need to specify a particular madhhab (definition) when concluding a marriage contract. Mentioning the Shafi'i madhhab in the contract does not obligate you to follow it in all matters of marriage and divorce. You are permitted to follow other scholars and to adopt the view of those who say that your divorce did not occur. It is permissible for someone afflicted with obsessive thoughts to adopt the easiest of the differing opinions. It is advised to disregard obsessive thoughts about divorce and other matters and not to pay attention to them.