A company that is asking me to joining immediate...

Thanks for joining and trusting us, much appreciated!

We would like to inform you that if you mean the employer, then you have to file a complaint in the Ministry of Human Resources and Emiratisation and clarify the reasons of the complaint and attach the documents that prove your complaint. The labor office will hear the employer, then they will decide and issue the verdict or refer it to the labor court.

 you shall inquire through the Ministry of Human Resources and Emiratisation website:

According to the given facts and for clarification purposes, we would like to explain to you,
You can transfer the visit visa to a work visa, but you have to obtain the approval of the ministry of labor and social affairs. Knowing that, the employer / company shall apply for this approval.
Article 42 of the Foreigners residency law in the UAE stipulates on the conditions in which, the foreigner can transfer a visit visa to a tourist one:
The changing of foreigners' status in the country must come under permits for entering the country for visit or work:
The foreigner must obtain an approval from the ministry of labor or an approval from official authorities outside the law scale. This is in order to be registered on the same sponsor whom your visa is attached to. 
Paying the pardon fees from the leaving conditions set by councils of ministers no.6 in 1994, which stipulates in regard of amendments on the payment fees' mechanism in the Administration of passports and citizenship. This is in case of being an employee at the private sector.