1. yes the email correspondences can be treated as valid contract
2. however i suggest that since 70% work is done, you can agree for a last time to extend the completion date
3. i can understand your concern but i am saying the above for a reasons
4. if you decide that you want to take legal steps against the contractor, then the litigation will not come cheap
5. you will have to spend again on that which is a stressor
6. yes, had the contractor not completed even 50% work, then it was altogether another thing. In that case, you could have definitely taken legal steps to claim a refund
7. suppose you take legal steps and issue a threatening legal notice to complete the project within the period stated in that notice or to claim refund, then that would unnecessarily create bitterness and the contractor would also contest your claim
8. on the other hand, i suggest that you issue them a legal notice through a lawyer but the words therein have to be balanced so that it does not sound threatening but only an intimation of giving them a last chance to complete the project by the agreed date stated in the notice
9. however please note that if your grievance is also that the contractor has done a shoddy job or the job done does not live to your expectations and instructions given before commencement of work, then you are entitled to claim refund with damages. But in your query i do not see that such is your grievance