It happens sometimes, when we are removing any packages using apt-get remove command its doesn't delete everything. And as a result when we are installing it again we are not getting completely fresh installation rather it uses old configuration etc.

To to avoid this situation we can use --purge argument with apt-get remove. 

apt-get remove --purge 'mysql-server.*'

This command will remove mysql related packages completely from the system. you should also run below command to remove unnecessary packages.

apt-get autoremove

To install missing packages run this command.this command will install missing packages if is there any. 

apt-get -f install