Contact the actual property owner. Just say you want to make sure your bid has been passed on to them, as an estate agent has let you down before. Fair chance they will give some useful comments about your bit or others,
A family member found out this way that her estate agent was not passing on bids - in order to sell her house cheap to his builder mate, the 'only' person to have made an offer on the property, or so the agent had claimed....