It is possible to suspend the ADSL service for a few months - I do not know how many. My sister took out the telephone line and ADSL for me ( before I got residency) and it is still in her name although I pay the bills; she has to make any changes to the account and is liable for payment (good job she trusts me - this is important). Last year I was away for 4 months and we suspended the service for 3 months. So, it is possible to suspend the service but I don't know how you go about it.
One important point , which I have mentioned before, is that LIMITSIZ does not do what it says on the tin. One version of LIMITSIZ gives you a maximum download limit of 50Gb, after which your download speed drops right off. The true UNLIMITED version of LIMITSIZ (which gives you unlimited downloads) costs 93 TL per month. Believe me , I found this out the hard way and spent weeks talking to the TTNET English helpline about why my speed kept dropping before I got through to someone who actually knew what was going on.