They can take advantage of multiple antennas, directional antenntas, or both to lock onto the interference sources as well as the intended signal and use DSP to subtract out the noise and recover the original signal. Others have posted about how cellphones can take advantage of multipath interference to actually improve the received signal rather than degrade it. As long as the enemy is using a small number of stationary or slow-moving transmitters for their interference, you can locate them all and use DSP to remove the noise, OR if you can arrange for your signal to arrive from a different direction than the enemy's jamming just use a directional antenna.
It would get more difficult if the enemy had hundreds of jamming transmitters moving around and covering your receiver from all directions. In the case of jamming a drone, your enemy would need either space-based jammers or airborne jammers to cover you from above. Space based jammers are impractical though (because of the distance) and airborne jammers are laughably easy to shoot down. It seems to me that the simple solution is to deliver your signals from above (satellites), use a directional antenna to ignore noise coming up from the ground, and then shoot anything out of the sky that makes noise which interferes with your signal.