All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, you should know that it is an obligation on the children to spend according to their ability on their poor parents. However, if the parents are not poor or that the children are insolvent, then they are not obliged to spend on their parents. If this is the case about the obligatory spending, then it is more appropriate that it also applies to the non-obligatory spending. Nonetheless, the children should endeavour to be kind and dutiful to them as much as possible.
Therefore, we advise you to try your best to convince your parents and clarify to them your situation.
First, you should seek the help of Allaah then the help of whoever could influence them. If they are convinced, all perfect praise be to Allaah, otherwise you are not sinful for not pleasing them.
Allaah says (what means): {Let a man of wealth spend from his wealth, and he whose provision is restricted, let him spend from what Allaah has given him. Allaah puts no burden on any person beyond what He has given him. Allaah will grant after hardship, ease.} [Quran 65:7]
Anyway, you have to be keen on being kind to your parents and pleasing them at all times.
Allaah Knows best.