Many thanks for your patience, I am pleased to be able to continue assisting with your query now. First of all, I am sorry to hear about the issues you have experienced in your situation.
Your main argument here would be that you were constructively dismissed. This occurs when the following two elements are present:
- A serious breach of contract by the employer; and
- An acceptance of that breach by the employee, who resigns in response to it.
Whilst the alleged breach could be a breach of a specific contractual term, it is also common for a breach to occur when the implied term of trust and confidence has been broken. This is an implied term, of a contractual nature, which automatically exists in every employment relationship. It is there to ensure that the employer and employee treat each her fairly and reasonably. The breaches that could qualify could be a serious single one, or a series of less serious, but still relevant breaches over a period of time, which together could be treated as serious enough (usually culminating in the 'last straw' scenario).
Constructive dismissal has the effect of voiding the whole contract between you and the employer because they have acted in serious violation to start with and that breach voids the contract, allowing you to leave as you are no longer bound by it. So you would be arguing that the repayment clauses, which formed part of the contract, are now also void as a result.
Unfortunately there is nothing stopping the employer from taking this further as each side has their own argument they are free to pursue. However, if they do, the above is your main defence.