BITMAP AND Is Not Being Used

I have 2 sets of phone number ranges and need to find the ranges that intersect.

create table rng1
(
rng_start varchar2(10),
rng_end varchar2(10)
);
[code]....

When I try to find the ranges matching (intersecting) a certain range (e.g. '21112'-'2111299999'), optimizer does a FULL TABLE SCAN, which is not opimal in my opinion. I use the hint to force the optimizer use the indexes.

select /*+ index_combine(rng2 x_rng2_start, x_rng2_end) */ *
from rng2
where
rng2.rng_start <= '2111999999'
and rng2.rng_end >= '2111';
Plan
SELECT STATEMENT ALL_ROWSCost: 60 Bytes: 17,344 Cardinality: 1,084
7 TABLE ACCESS BY INDEX ROWID TABLE LUMAMIPA.RNG2 Cost: 60 Bytes: 17,344 Cardinality: 1,084
6 BITMAP CONVERSION TO ROWIDS
5 BITMAP AND
2 BITMAP MERGE
1 BITMAP INDEX RANGE SCAN INDEX (BITMAP) LUMAMIPA.X_RNG2_START
4 BITMAP MERGE
3 BITMAP INDEX RANGE SCAN INDEX (BITMAP) LUMAMIPA.X_RNG2_END

However, when I try to join the 2 sets of ranges by matching the intersecting ranges, then the range scan and "BITMAP AND" of the 2 indexes is not done, even though the hint is specified:

select /*+ index_combine(rng2 x_rng2_start, x_rng2_end) */
count(*) cnt
from rng1
join rng2 on
rng1.rng_start <= rng2.rng_end
and rng1.rng_end >= rng2.rng_start;
[code]...

How to make the optimizer use the range scan of both indexes? Is there a better way to match the ranges?