Did you try requesting a higher cruise altitude in the ATC dialog window? You can ask in increments of up to 10,000 feet: so if they put you at 16,000 you can request FL260, then FL360.
Note that if you’re on a westbound flight you can’t get FL370, as cruise altitudes are staggered; odd thousands for IFR go to eastbound flights (magnetic course from 0 to 179 degrees) and even thousands go to westbound flights (course from 180 to 359 degrees).
For the full rules (in the US, which are based on the ICAO international rules I believe) see eCFR :: 14 CFR 91.179 -- IFR cruising altitude or flight level.
(Note that VFR flights go on 500-foot offsets from that.)