Firstly do take advice from a lawyer in British- Spanish law, just in case preferably in the UK.
I am not an expert on Spanish law as it seems no one really is as it varies every year and depends who one is dealing with, town hall, local government etc. After many years here it does seem the law of the jungle operates and that the “big boys ” are favoured ,ie banks and developers.
The bank cannot touch your house I would have thought but for goodness sake pay the mortgage every month even if you have to live on bread and dripping for the month. Do not fall into arrears as they will have you by you know what. Check your bank statement religiously just to make sure that the bank has n´t forgotten to charge the monthly payment. I assume the bank with which you have the mortgage is the same as you have your current account and that it debits your account each month. Also was your P60 OK or did the agent make that more attractive than it should have been?. This could lead you into trouble. Do not let your account go into the red, and as I said before check your bank statement carefully. Do you have an internet account with them? if not open one so that you can check your position every day.
Try to think of every avenue that the bank could use to put a charge on your property.
Spanish law moves very slowly and if they did try to bring a case against you it would take years to come up. Although it would be something hanging over you.
Normally I would recommend you sell the property and get rid of the mortgage just in case, the way the market is at present that is easier said than done.
I may seem cynical but I have known of things being done by town halls,developers, banks that would have lead to them being in prison anywhere else in the world.
In my experience of helping people , Spanish companies like to threaten . A friend of mine received a letter from a debt collection company representing Digital Plus one of the cable operators here asking for payment of a satellite dish they had provided some years before. The person who had contracted the satellite service was my friends wife and she had been dead for seven years and had only contracted the service
about six months before she died. I wrote to them in Spanish explaining that their client had died, enclosed a copy of the Spanish death certificate ,every month thereafter a copy of the same letter came.For two months I sent a copy of my previous reply then phoned the company and told them the position, the guy I spoke to basically said they never take any notice of replies and keep on writing , quite often the person receiving the letter gives up and pays up.
Good luck, please do take top advice from an international lawyer. Do not listen to know it alls and bar room lawyers, advice here is 2 a penny and worth less.