ORDER BY text doesn't use my index?!
You can find the answer in the EXPLAIN ANALYZE outputs you've posted.

In the first one, the estimated cost of the sequential scan is 96.24, while the index scan has a cost of 360.41 in the second one.  This is why the planner decided not to use the index.

However, we see that the execution time is much better in the second case.  The main reason might be that the row estimate of the sequential scan is quite bad - 15 rows are expected instead of ~3k.  Do an ANALYZE crm_customer; and see if it changes - it is already possible that the index will be chosen.