Sounds like computergeek has the right idea if you had the $10 every month promo, unless you are referring to the $10 referral credit in which case that's a one time thing.
Hey, I'm not sure if it can be done but you may want to try this suggested solution from a similar situation. https://productioncommunity.publicmobile.ca/t5/Plans-Add-Ons/Can-t-incrementally-upgrade-my-plan-without-full-charge/m-p/404304/highlight/tr...
Something similar happened to me, I was sending texts but the other person didn't receive them. He had a work number and personal number and I had started a SMS chat to his work number that he got rid of so obviously he wasn't receiving the messages ...
I think the only way would be to contact a moderator and ask, hopefully they are able to help reverse that. I don't know of any self serve way to do this. Good luck!