Park Direct, DRP, Zenith & Gladstones

Hi everyone. I've only just discovered this forum and, consequently, I think I can now see some light at the end of the tunnel.
I received a PCN from Park Direct in June 2016. I duly waited for the NtK to arrive and then I wrote to them twice to inform them that their claim for cash was not valid. I gave them at least three reasons and enclosed all the evidence. As expected, their reply was that they still wanted money. They did not refute any of my assertions or evidence, but stated that they would pursue their claim on the grounds that I did not appeal within their 28 day limit. There followed a string of begging letters containing all sorts of exciting discounts and offers. They then passed the "debt" on to DPR who then passed it on to Zenith (despite them being one and the same). I responded to Zenith's demand with a letter informing them that I disputed the claim. Needless to say, that fell on stony ground. After a hiatus of several months, I have suddenly received a letter from Gladstone "solicitors" advising me to pay up. In the letter, they state that they MAY advise their client to instigate court proceedings.
Having seen all the sound advice on this forum, I wouldn't be particularly bothered if they did. However, my initial question is simply how do I hold them off for a couple of months? I'm going on holiday soon and I really don't want to come back and find that they've instigated court proceedings against me in my absence and that I'm too late to file a defence. Any help with likely timescales would be much appreciated.