Are you afraid that someone is tracking your phone? There are a few ways of making sure if that takes place and protecting yourself from further redirected calls
1. Type codes *#21# and *#62# into the phone, confirm with a call number. The first command will tell you, if you received any redirected calls; second one will tell you, where did these calls come from.
2. If you want to get rid of unwanted redirected calls once and for all, type in the code ##002#. This will block any redirected calls from your phone.
3. If you only want to block a certain number (only on Android), you must go to your list of calls and select the annoying number. Touch it and select Specifics option. Now select the three dots icon and select Block the number option. If you want to unblock it later, repeat your steps and remove the number from blocked list by touching the minus
Voila, that is that for those pesky telemarketers ;).