Right of a partner to withdraw from partnership without fulfilling obligations

Hi,

We have created a business under LLC with a local partner.

It's been two months into preparations and approximately one month ago, the partner backed out of the agreement and requested her money back of investment.

Since the date of this request, she has gone on to ignore us and prior to this request it led to every action of ours has been ignored.

She accepted the terms of backing out and her payment via a post-dated cheque yet the partner has continued to ignore us yet again.

Now my wife and children's visa and health insurance rely on this and the current visa is due to run out. How do I confront this?