Merck KGaA interview questions

The interview process involved six 1:1 meetings for about three months. The Merck team involved was from HR recruiter to CMO and Global VP. The process was long. Some of the interviews were structured and run very professionally, some of them highly informal, with the manager talking for about 40 minutes before asking me any question! In the end they made me an offer and everything became highly unprofessional at that moment. The offer was 15% lower than what I asked during the interviews and they tried several times to negotiate it mentioning that I would get a performance bonus of 17% at the end of the year to compensate up to the amount I requested (the performance bonus yet was not guaranteed). Particularly the recruiter was highly unprofessional via mentioning at least 4 times in a call that "this is our last offer", "if you don't accept it, we will start recruiting as of the next day". Also, the recruiter refused to put the details of the offer in written justifying it by "what I am telling you by phone should be enough". When asked, the recruiter told me that the company does not have Intent Letters or written documents for making a job offer.