[disclaimer: im not a lawyer lmao if i was i would be out making money rn]
have the songs been released, and if so, are you set up with a Performance Rights Organization like ASCAP?
if so, how long has it been since the songs came out?
does the contract specify when you get paid by?
as a rule, in any creative industry, if a client is telling you "don't worry, just trust me," that's
a HUGE HUGE HUGE red flag. people (even within the industry) don't always respect the work that goes into what you do. press them for specifics. you need to put food on your table just like everyone else. double check the contract, see if there are payment dates set up. if you can talk to them in person, do that (if not, maybe skype/facetime/ phone call).
more importantly, if you have the resources available, i'd recommend talking to like, an actual lawyer about best practices for songwriting. especially if you plan on pursuing ghostwriting further.