I'm pretty sure if you sign that settlement agreement, and they don't pay you the refund, it is unenforceable and the settlement agreement to not sue is invalid.  I'm not any attorney, and since your contacting one anyone, check with them and sign the agreement if you still can or are advised to do so.

10. Contract Construction. In the event that any provision(s) of this Agreement shall be held invalid or unenforceable by a court of competent jurisdiction or by any future legislative or administrative action, such holding or action shall not negate the validity or enforceability of any other provisions hereof. The word “or” as used in this Agreement has the meaning equivalent to “and/or”. The terms ‘include’, ‘includes’ and ‘including’ will be deemed to be immediately followed by the phrase “without limitation.” If a party is the subject of a sentence, then the word “will” expresses an obligation, and deemed equivalent to “shall”. The parties agree the rules contract interpretation that would otherwise require ambiguities to be construed against the drafting party will not apply to this Agreement. These Terms are in the English language only, which language will be controlling in all respects. Any versions of this Agreement in any other language will be for accommodation only and will not be binding upon either party. All communications and documentation to be furnished under this Agreement will be in the English language.