Right, this is a bit of a mess frankly.
The issue is when the tenancy ceased. If you expressly agreed to a further 6 months tenancy upon the previous one having expired then you will be bound to pay the rent until the term expired and you vacated (for which you would not have had to give notice to the landlord) or until you vacated the property if longer.. Note though if you occupied the property after the fixed term expired then you would have done so under a statutory periodic tenancy, this means that you would have had to have given one months notice with such notice expiring on a rent day.
The landlord's are not under an obligation to see that a new 6 months tenancy is executed upon the previous one ceasing, they can simply permit the occupation to carry on as a statutory periodic tenancy.
Very broadly, if the landlord accept that the tenancy is terminated at a certain date and you do not dispute the date of this suggested termination but have not paid rent then you will be bound to pay the rent and they could sue you for it and probably will.
The deposit is a separate issue and you should correspond with them on the this issue as to what they suggest by way of a return. If you dispute the amount that is suggested to be returned to you then the scheme will run a dispute resolution service which you can avail yourself of.
You've got to engage with the agent/landlord otherwise they will just issue and you will have to dispute it at hearing, which will be time-consuming and stressful. You should try to avoid this, they will want to as well.
The contacting of your mother's is sharp practice but the practical reality is that you have not suffered any financial loss as a result for which you could sue unfortunately.
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