I would suggest pitching to publishers rather than the artists directly - either as well as or as an alternative strategy
You have done exceptionally well to get 1 song picked up
The trouble with pitching directly s that you may not have a "quality control" mechanism as part of the process
I can say this as I haven't heard your stuff yet - but have you considered it isn't good enough?
By pitching to publishers if you get some interest you can work on forming relationships, get feedback, and work together to fine tune your pitches
Pitching directly to artists has the potential of getting a bad reputation with them as they may see you as "pestering"
Many artists/management would not even entertain an "unsolicited" pitch so you could be wasting time, money and energy
There is also a certain way of conducting a "pitch" - are you "selling" in the right way, how good is your covering letter etc ?
It is also all about "timing" - are you pitching at just the right time when an artist is actually looking for material?
Are you pitching to artists that perform other people's material?
There are lots and lots of different factors involved that would improve your chances - a good publisher would know all of the these "tricks" and should have built up contacts and relationships to exploit these opportunities when the come up
There are pitching services available (Taxi, Audio Rokit, SongLink etc.) so these may be worth investigating
You are clearly doing something right as you have sold a song so I would take encouragement from that
The only other thing I would add is that everything in the music industry seems to take a loooong time!
It is taking weeks and weeks for me to sort out a publishing deal that has been offered to me - they seem super keen but it is weeks between emails - so I do think it is a bit of a patience game as well!
I would suggest posting some track here in the reviews section for some "non-friends and family" feedback and I would really look forward to hearing them
Good luck