The most important thing is to clarify for yourself if it's your iPhone's internal storage that is full, or if it's indeed your iCloud storage that is full.
You can check your iPhone's local on-board device storage following these steps:
https://support.apple.com/en-us/HT201656
By local storage this refers to the specific model type of your iPhone, like if you have a 32GB, 64GB, 128GB, or 256GB model, for example.
And you can check your Apple ID's iCloud storage usage here:
https://support.apple.com/en-us/HT201318
By iCloud storage this refers to if you're on the free 5GB plan, or the paid 50GB, 200GB, or 2TB plan, for example. Since you mentioned 99-cents a month, it sounds like you're on the 50GB plan.
Depending on the results (i.e. if your out of local iPhone storage versus out of iCloud storage) and what you want to do, that will affect how you need to move forward.
You can cancel, downgrade, or upgrade your iCloud storage plan... if that's actually the specific issue following the steps here:
https://support.apple.com/en-us/HT207594
To avoid data loss though, you don't want to carelessly cancel an iCloud storage plan if you would be over your free 5GB iCloud storage limit without planning accordingly in advance to move your iCloud data to your iPhone...if your iPhone would have enough physical space to accommodate the amount of data in question. Thus, it's important to be very clear if it's local iPhone or iCloud storage that you're hitting the limits of.
Most people get confused by the fact their local iPhone (64/128/256GB) storage is full, and they try to resolve this "storage is full" warning through buying more iCloud storage, and don't actually switch to using more data to specifically use iCloud. This may or may not be what is going on with you specifically.
If this doesn't clarify the issue enough I suggest posting a screenshot here of the results of checking your local iPhone current storage and availability, as well as your iCloud storage use and availability.