Some good advice here. I understand that it’s so stressful for you, but try and focus on what you can do yourself to retain control.
There are three tenancy deposit schemes. Look them up and speak to each one, then get the details and let them know that you want to make a claim. They will email you a reference number and password for the deposit (belatedly) paid for your tenancy.
Honestly, stop contacting the agent and landlord as you can’t rely on their information. Remember that they are in opposition with you and will continue to respond only in ways to influence you to serve the landlord’s interests.
Do you have a copy of the certificate? It should state the dates when the tenancy commenced - check whether it is correct. Once you access the portal for the deposit scheme, you can send photos, emails and any information you want to be considered.
Try and give factual rather than emotional information. Were any inventories done and signed by you and the landlord to agree the condition of the property? If not, Do you happen to have any emails or evidence of the condition of the property when you signed the tenancy and surrendered it on returning the keys?
Did the landlord also provide you with what’s called ‘prescribed information’?
I have been in this situation myself and helped others through what seems like a scary process. Try not to panic, youre in a stronger position than you realise.