Lump Sum payment

Hi everyone, I am based in a UK Doctoral project that funded 14 Marie Curie fellows including myself. Our contracts ended in April and we have been payed our last salaries.However we still have not received our lump sum payment. We are not sure what that lump sum will include exactly apart from exchange rate related issues. Our host institute has made very interesting shifts in our payments during the 3 years. Exchange rate re-calculated in the end of 2 years and suddenly we found ourselves in the next band of payment and hence ended up paying a lot more taxes..We also had some differences between payment of each individual fellow. So we are expecting to be compensated on that in our lump sum. We are also expecting to be compensated on the exchange rate drop during these 3 years. Despite our contracts ending in April we still did not get our lump sump payments and our finance department is quite reluctant to inform us on specifics of the calculations of lump sum. A tentative letter of payment was sent to some of us, but we objected to that letter because there was no explanation on what is payed for what reason. Also, there was a huge difference between what we actually payed in our overall salaries and what is reported there that we were payed overall..After these issues they agreed to work more on the calculations. But everything is very unclear for us still. For instance, we still don't know if we will be compensated for the exchange rate drop. We still don't know why our overall salaries are reported to be larger than what we were actually payed. My first question is, is there any regulation that we can share with them to make them act faster on this process? It is quite concerning that they are keeping large amounts of money for long time. My second question is, is there any rule or regulation that will help us while we are trying to learn the specifics of these lump sum calculations? Is it written anywhere that MC fellows should be informed on these decisions? We have received payroll documents on the specifics of our salary, why not we also receive a similar document for lump sum My last question is how can we defend ourselves in terms of exchange rate loses? Again, is there any rule or regulation that we can rely on? Any article or any official person that can help us during this battle?:) Many thanks.