CST paid @ 5% & refund of 3% after submission of C Form

Dear Experts,

We paid the to Vendor CST @ 5%, later we will get 5% refund on submission of C Form.

But this time, due to delay from our side, we were delayed in submitting C Form & now the supplier is saying that he paid total 5% CST to govt. & no refund will come to us.

When asked to show proof that he deposited or not, he is rejecting to show the details.

Could any one please confirm:

1. Is there any alternative to get refund?

2. How to know whether vendor has really deposited the CST amount to govt. which includes our amount also?

3. Time period within which we can get refund, from the date of CST paid by the Vendor to the govt.

Pls clarify, it's urgent.

Thanking you in advance,