If you have £7K available & debts of £16K and have offered 43% then I assume you've no more money to use to increase your offer. I would not go back to them - at present just go on with the £5 p mth - but you may find they go to Court for a CCJ if you've told them the money for the full and final offer is yours, rather than (say) help from family.
There are a number of ways to play this, depending on your circumstances and what the other creditors reaction to your offer is.
In some situations you might qualify for a Debt Relief Order I can't set out all the criteria here & they are changing in October, but you would have to have made pro-rata payments to your creditors which reduce your capital below £1000. Also you must not own a property (even with a mortgage) or have other assets (such as a car) worth more than £1000. Look the subject up on the internet & contact your local CAB for more detailed advice if you think it might be a means of getting debt free.