The number of sources you can track will depend on the team plan and the limit is for the entire team, not an individual.
There are two numbers in Appbot for sources:
1 – number of sources you are tracking and
2 – the total number of sources tracked by all team members.
If you have stopped tracking a source, but the total team source number has not changed it means that another team member may still tracking that source or has added another one source to the account already.
To check which sources your fellow team members are tracking check out Team Sources.