I get a whole lot of text messages from this number everyweek. I pay for every single text message. When I call back, it says that this number is not accepting calls.

Text messages are about some fund raising event.

Call your phone service provider, as these are unwanted and costing you money. They should recognize any incoming messages from the solicitor and be able block / not charge you for them. Find out which company is sending these out and notify them ASAP. Charging YOU for THEIR advertisements is illegal. Keep that in mind.