BFL TRACON Controller reported an aircraft going below the MVA and was unable to communicate with the aircraft due to spotty radio coverage at the aircraft's altitude.

Narrative

I was working South Radar combined with all the sectors in the TRACON; I took an IFR handoff from JCF in the area of WJF Airport. I looked back after working other aircraft and Aircraft X was below the MVA. He was level at 080 and was in a 090 MVA. I heard the aircraft check in but couldn't hear me. I called JCF to ask what their MVA is in that area with hope that it was a valid altitude to assign and they said something along the lines of he's my control to climb. I tried to reach out multiple times to contact the aircraft and no response - I think he was too low for my radio coverage. I reached out on Guard to climb the aircraft; no response or ident. The aircraft went back to previous frequency and I believe got control instructions to climb. Once they were about 085-087 the pilot was able to hear me. After flying about 20 miles the aircraft asked if he did anything wrong. The pilot claimed he had a much different route filed but the controllers gave him direct.[I recommend to] appropriately staff the FAA's facilities so simple mistakes don't get overlooked.