Assuming that the original work was distributed under the GNU GPLv2, and that you have made a work which is a derivative of it (in copyright terms), you may redistribute your derivative work subject to GPLv2 ss 2 and 3.
The point of distributing under the GPL is to enable a work to continue to be used and/or repurposed by as large a number of people as possible. That said, in my experience people and organisations do occasionally release under the GPL without fully understanding what they are permitting1. Sadly for them, there are no take-backs from people who have already acquired a copy under those terms (see eg my article: "the license is irrevocable once even partial performance has occurred").
In this case the licensor seems to be unwilling, so you will need to be very, very sure of your grounds before you proceed. Read the section entitled "How to Apply These Terms to Your New Programs" at the end of the GPL. If the licensor has done everything the GPL recommends, you have good grounds for believing that the work was licensed to you on those terms. If, by way of example on the other hand, you downloaded it from a page titled "Here's our GPL software" but the code made no mention of that, then you might want to be a great deal more hesitant. If anything of significance (eg your business, or your house) rests on this you will want to take professional legal advice, which this is not, before proceeding.
But assuming you do proceed, then as long as you obey the requirements of GPLv2, particularly ss 2 and 3, with respect to your derivative work, then you should be OK.
1See by way of example the sad fate of SleepyHead, wherein the highly-dedicated lead developer generously published his work under GPL, putting in thousands of hours of his own development time while failing to understand how free software development works. He then completely lost it when other people dared to take the current code and release it. He halted all development and walked away from the project (as is completely his right), concluding "Friends don’t let friends release full blown complex applications under the GPL".
Final note for anyone interested in sleep apnoea and free software: the fork survived and is doing nicely, at https://gitlab.com/pholy/OSCAR-code .