I got a job at a company last week, they sent me an offer letter and I responded back to them with an acceptance mail the very next day. In the offer letter it was written that if you did not respond back with the signed offer letter within 3 days the offer may be withdrawn. Here's the thing, this is my first job change so I don't know how these things work.
I called up HR the very next day and told them I would be sending the signed offer letter next week as I had to mention the joining date in the offer letter and I thought I would have to resign first at my current job and get a relieving date from them before I can give a joining date to the new company. The HR person agreed.
I sent them the signed offer letter 5 business days after they extended the offer and HR has been unresponsive to phone calls and emails ever since (for a week).
I'm concerned whether they have blocked me because I've extended their deadline or they have given the job to somebody else or the job doesn't exist anymore. I have no clue what's going on and what I should do? I have already resigned from my current job and I'm worried.