Unable to pay my maintenance fees after 17 years, what can I do?

I can no longer afford my timeshare week as it has gone from £500 to £617.62. I have had it for 17 years and now only have my state pension.
I have called the office twice, emailed 3 times & explained this and told them I have to give it up & asked how to go about this. So far I have not had any response.
Any advice would be great.